{"id":100178,"date":"2026-02-15T20:25:18","date_gmt":"2026-02-15T20:25:18","guid":{"rendered":"https:\/\/vibromera.eu\/?post_type=calculator&#038;p=100178"},"modified":"2026-07-02T19:37:45","modified_gmt":"2026-07-02T19:37:45","slug":"oil-viscosity-temperature","status":"publish","type":"calculator","link":"https:\/\/vibromera.eu\/tl\/calculators\/oil-viscosity-temperature\/","title":{"rendered":"Oil Viscosity\u2013Temperature Calculator | Walther ASTM D341"},"content":{"rendered":"\n<script type=\"application\/ld+json\">{\"@context\":\"https:\/\/schema.org\",\"@type\":\"WebApplication\",\"name\":\"Oil Viscosity\u2013Temperature Calculator\",\"description\":\"Calculate kinematic viscosity at any temperature using Walther equation. VI per ASTM D2270. ISO VG classes.\",\"url\":\"https:\/\/vibromera.eu\/calculators\/oil-viscosity-temperature\/\",\"applicationCategory\":\"Engineering Calculator\",\"operatingSystem\":\"Any\",\"offers\":{\"@type\":\"Offer\",\"price\":\"0\",\"priceCurrency\":\"EUR\"},\"creator\":{\"@type\":\"Organization\",\"name\":\"Vibromera\",\"url\":\"https:\/\/vibromera.eu\/\"},\"datePublished\":\"2024-01-01\",\"dateModified\":\"2025-06-01\",\"inLanguage\":\"en\",\"isAccessibleForFree\":true}<\/script>\n\n<script type=\"application\/ld+json\">{\"@context\":\"https:\/\/schema.org\",\"@type\":\"FAQPage\",\"mainEntity\":[\n{\"@type\":\"Question\",\"name\":\"What is the Walther equation?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"The Walther (ASTM D341) equation: log log(\u03bd + 0.7) = A \u2212 B \u00d7 log(T), where T is in Kelvin. It produces a straight line on ASTM viscosity-temperature paper. Accurate for mineral oils from -20\u00b0C to 150\u00b0C.\"}},\n{\"@type\":\"Question\",\"name\":\"What is Viscosity Index (VI)?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"VI indicates how much viscosity changes with temperature. Higher VI = less change. Mineral oils: VI \u2248 80-100, synthetic PAO: VI \u2248 120-160, multigrade engine oils: VI > 150.\"}},\n{\"@type\":\"Question\",\"name\":\"What is ISO VG classification?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"ISO VG classifies industrial lubricants by kinematic viscosity at 40\u00b0C. VG 32 means \u03bd\u2084\u2080 \u2248 32 cSt. Range: VG 2 to VG 1500.\"}},\n{\"@type\":\"Question\",\"name\":\"How accurate is the Walther equation?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"Very accurate for mineral oils (-20 to 150\u00b0C). Less accurate for synthetics, very low temps (near pour point), or very high temps (near flash point).\"}},\n{\"@type\":\"Question\",\"name\":\"What is the optimal operating viscosity range?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"Most bearings and gears operate optimally at 13-100 cSt. Below 13 cSt: boundary lubrication risk. Above 100 cSt: excessive churning losses. Exact range depends on application speed and load.\"}}\n]}<\/script>\n\n<link rel=\"preconnect\" href=\"https:\/\/fonts.googleapis.com\">\n\n<link rel=\"preconnect\" href=\"https:\/\/fonts.gstatic.com\" crossorigin>\n\n<link href=\"https:\/\/fonts.googleapis.com\/css2?family=DM+Sans:ital,opsz,wght@0,9..40,300;0,9..40,400;0,9..40,500;0,9..40,600;0,9..40,700;1,9..40,400&#038;family=JetBrains+Mono:wght@400;500;600&#038;family=Fraunces:opsz,wght@9..144,700;9..144,800&#038;display=swap\" rel=\"stylesheet\">\n\n<link rel=\"stylesheet\" 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16px;font-size:13px;color:var(--vc-ink-muted)}.vc-footer a{color:var(--vc-accent);text-decoration:none}.vc-footer-links{margin-top:8px;font-size:12px}.vc-footer-links a{margin:0 8px}\n@media print{.vc-section-body{max-height:none!important}.vc-faq-a{max-height:none!important}.vc-results{max-height:none!important;padding:24px!important}.vc-copy-btn,.vc-section-chevron,.vc-faq-chevron,.vc-presets,.vc-promo{display:none!important}}\n.vc-viz{margin:20px 0;background:var(--vc-surface);border:1px solid var(--vc-border-light);border-radius:var(--vc-radius);padding:16px;overflow:hidden}.vc-viz svg{width:100%;height:auto;display:block}.vc-viz-title{font-family:var(--vc-mono);font-size:11px;font-weight:500;letter-spacing:0.1em;text-transform:uppercase;color:var(--vc-ink-muted);margin-bottom:12px}\n<\/style>\n\n<div class=\"vc-calculator\" id=\"vc-oil-visc\">\n<header class=\"vc-header\"><p class=\"vc-header-eyebrow\">Free Engineering Tool<\/p><h1 class=\"vc-header-title\">Oil Viscosity\u2013Temperature Calculator<\/h1><p class=\"vc-header-subtitle\">Calculate kinematic viscosity at any temperature using the Walther (ASTM D341) equation. Viscosity Index per ASTM D2270. Optimal operating range and pour point estimation.<\/p><div class=\"vc-badges\"><span class=\"vc-badge\">Walther \/ ASTM D341<\/span><span class=\"vc-badge\">Viscosity Index<\/span><span class=\"vc-badge\">ISO VG<\/span><span class=\"vc-badge\">Pour Point<\/span><\/div><\/header>\n\n<div class=\"vc-card\">\n    <form class=\"vc-form\" id=\"vc-form\" autocomplete=\"off\">\n        <div class=\"vc-form-grid\">\n            <div class=\"vc-field\"><label class=\"vc-label\" for=\"vc-v40\">\u03bd at 40\u00b0C <span class=\"vc-label-hint\">(cSt = mm\u00b2\/s)<\/span><\/label><input class=\"vc-input\" type=\"number\" id=\"vc-v40\" step=\"any\" value=\"68\" placeholder=\"e.g. 68\"><\/div>\n            <div class=\"vc-field\"><label class=\"vc-label\" for=\"vc-v100\">\u03bd at 100\u00b0C <span class=\"vc-label-hint\">(cSt)<\/span><\/label><input class=\"vc-input\" type=\"number\" id=\"vc-v100\" step=\"any\" value=\"8.7\" placeholder=\"e.g. 8.7\"><\/div>\n            <div class=\"vc-field\"><label class=\"vc-label\" for=\"vc-tgt\">Target Temperature <span class=\"vc-label-hint\">(\u00b0C)<\/span><\/label><input class=\"vc-input\" type=\"number\" id=\"vc-tgt\" step=\"any\" value=\"60\" placeholder=\"e.g. 60\"><\/div>\n            <div class=\"vc-field\"><label class=\"vc-label\" for=\"vc-vg\">ISO VG Class <span class=\"vc-label-hint\">(auto-fills \u03bd40\/\u03bd100)<\/span><\/label><select class=\"vc-select\" id=\"vc-vg\"><option value=\"\">\u2014 Custom \u2014<\/option><option value=\"10\">VG 10<\/option><option value=\"15\">VG 15<\/option><option value=\"22\">VG 22<\/option><option value=\"32\">VG 32<\/option><option value=\"46\">VG 46<\/option><option value=\"68\" selected>VG 68<\/option><option value=\"100\">VG 100<\/option><option value=\"150\">VG 150<\/option><option value=\"220\">VG 220<\/option><option value=\"320\">VG 320<\/option><option value=\"460\">VG 460<\/option><option value=\"680\">VG 680<\/option><option value=\"1000\">VG 1000<\/option><option value=\"1500\">VG 1500<\/option><\/select><\/div>\n        <\/div>\n        <div class=\"vc-presets\"><div class=\"vc-presets-label\">Quick presets<\/div>\n            <button type=\"button\" class=\"vc-preset-btn\" data-v40=\"32\" data-v100=\"5.4\" data-t=\"60\" data-vg=\"32\">VG 32 @ 60\u00b0C<\/button>\n            <button type=\"button\" class=\"vc-preset-btn\" data-v40=\"68\" data-v100=\"8.7\" data-t=\"80\" data-vg=\"68\">VG 68 @ 80\u00b0C<\/button>\n            <button type=\"button\" class=\"vc-preset-btn\" data-v40=\"220\" data-v100=\"19\" data-t=\"50\" data-vg=\"220\">VG 220 @ 50\u00b0C<\/button>\n            <button type=\"button\" class=\"vc-preset-btn\" data-v40=\"460\" data-v100=\"31\" data-t=\"70\" data-vg=\"460\">VG 460 @ 70\u00b0C<\/button>\n        <\/div>\n    <\/form>\n    <div class=\"vc-results\" id=\"vc-results\">\n        <div class=\"vc-results-head\"><h2 class=\"vc-results-title\">Viscosity Results<\/h2><button type=\"button\" class=\"vc-copy-btn\" id=\"vc-copy-btn\"><svg width=\"14\" height=\"14\" viewbox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\"><rect x=\"9\" y=\"9\" width=\"13\" height=\"13\" rx=\"2\"\/><path d=\"M5 15H4a2 2 0 01-2-2V4a2 2 0 012-2h9a2 2 0 012 2v1\"\/><\/svg> Copy<\/button><\/div>\n        <div class=\"vc-result-grid\">\n            <div class=\"vc-rcard vc-rcard-primary\"><div class=\"vc-rcard-label\">Viscosity at Target Temperature<\/div><div class=\"vc-rcard-value\" id=\"vc-r-visc\">\u2014<\/div><\/div>\n            <div class=\"vc-rcard\"><div class=\"vc-rcard-label\">Viscosity Index (VI)<\/div><div class=\"vc-rcard-value\" id=\"vc-r-vi\">\u2014<\/div><\/div>\n            <div class=\"vc-rcard\"><div class=\"vc-rcard-label\">Operating Range Check<\/div><div class=\"vc-rcard-value\" id=\"vc-r-range\" style=\"font-size:14px\">\u2014<\/div><\/div>\n            <div class=\"vc-rcard\"><div class=\"vc-rcard-label\">Walther Constant A<\/div><div class=\"vc-rcard-value\" id=\"vc-r-A\" style=\"font-size:18px\">\u2014<\/div><\/div>\n            <div class=\"vc-rcard\"><div class=\"vc-rcard-label\">Walther Constant B<\/div><div class=\"vc-rcard-value\" id=\"vc-r-B\" style=\"font-size:18px\">\u2014<\/div><\/div>\n            <div class=\"vc-rcard\"><div class=\"vc-rcard-label\">Reference: \u03bd40 \/ \u03bd100<\/div><div class=\"vc-rcard-value\" id=\"vc-r-ref\" style=\"font-size:16px\">\u2014<\/div><\/div>\n            <div class=\"vc-rcard\"><div class=\"vc-rcard-label\">Estimated Pour Point<\/div><div class=\"vc-rcard-value\" id=\"vc-r-pour\" style=\"font-size:18px\">\u2014<\/div><\/div>\n            <div class=\"vc-rcard\"><div class=\"vc-rcard-label\">Dynamic Viscosity (\u03b7)<\/div><div class=\"vc-rcard-value\" id=\"vc-r-dyn\" style=\"font-size:18px\">\u2014<\/div><\/div>\n        <\/div>\n        <div class=\"vc-viz\" id=\"vc-viz\"><div class=\"vc-viz-title\">Walther Chart \u2014 Viscosity vs Temperature<\/div><div id=\"vc-viz-svg\"><\/div><\/div>\n    <\/div>\n<\/div>\n\n<div class=\"vc-section vc-open\" id=\"vc-sec-theory\">\n    <button type=\"button\" class=\"vc-section-toggle\" aria-expanded=\"true\"><span class=\"vc-section-toggle-text\"><span class=\"vc-section-icon\">\ud83d\udcd8<\/span><span class=\"vc-section-title\">Theory, Formulas &amp; ISO VG Table<\/span><\/span><svg class=\"vc-section-chevron\" viewbox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\"><path d=\"M6 9l6 6 6-6\"\/><\/svg><\/button>\n    <div class=\"vc-section-body\"><div class=\"vc-section-inner vc-theory\">\n        <h3>Walther Equation (ASTM D341)<\/h3>\n        <div class=\"vc-formula-box\" id=\"vc-katex-1\"><\/div>\n        <p>Where \u03bd is kinematic viscosity in mm\u00b2\/s (cSt), T is absolute temperature (K), and A, B are constants determined from two reference points.<\/p>\n        <h3>Viscosity Index (ASTM D2270)<\/h3>\n        <div class=\"vc-formula-box\" id=\"vc-katex-2\"><\/div>\n        <p>VI compares the oil&#8217;s viscosity-temperature behavior to two reference oils: L (VI=0, naphthenic) and H (VI=100, paraffinic). Higher VI = less viscosity change with temperature.<\/p>\n        <h3>Practical Example<\/h3>\n        <div class=\"vc-example-box\"><div class=\"vc-example-title\">Example \u2014 VG 68 at 80\u00b0C<\/div>\n            <p><strong>Given:<\/strong> \u03bd\u2084\u2080=68 cSt, \u03bd\u2081\u2080\u2080=8.7 cSt<\/p>\n            <p>Walther: A=9.3097, B=3.6244<\/p>\n            <p>At 80\u00b0C (353.15 K): log log(\u03bd+0.7)=9.3097\u22123.6244\u00d7log(353.15)=9.3097\u22129.2348=0.0749<\/p>\n            <p>\u03bd = 10^(10^(0.0749))\u22120.7 = <strong>14.7 cSt<\/strong><\/p>\n            <p>VI \u2248 98 (typical mineral oil)<\/p>\n        <\/div>\n        <h3>ISO VG Reference Table<\/h3>\n        <table class=\"vc-table\"><thead><tr><th>ISO VG<\/th><th>\u03bd at 40\u00b0C (cSt)<\/th><th>\u03bd at 100\u00b0C (cSt)<\/th><th>Typical Application<\/th><\/tr><\/thead><tbody>\n            <tr><td>VG 10<\/td><td>10<\/td><td>2.6<\/td><td>Spindle oils, hydraulics<\/td><\/tr>\n            <tr><td>VG 22<\/td><td>22<\/td><td>4.4<\/td><td>Hydraulic systems<\/td><\/tr>\n            <tr><td>VG 32<\/td><td>32<\/td><td>5.4<\/td><td>Hydraulic, light bearings<\/td><\/tr>\n            <tr><td>VG 46<\/td><td>46<\/td><td>6.8<\/td><td>Hydraulic, general bearings<\/td><\/tr>\n            <tr><td>VG 68<\/td><td>68<\/td><td>8.7<\/td><td>Heavy hydraulic, light gears<\/td><\/tr>\n            <tr><td>VG 100<\/td><td>100<\/td><td>11.4<\/td><td>Circulating, light gears<\/td><\/tr>\n            <tr><td>VG 150<\/td><td>150<\/td><td>15<\/td><td>Gears, bearings<\/td><\/tr>\n            <tr><td>VG 220<\/td><td>220<\/td><td>19<\/td><td>Industrial gears<\/td><\/tr>\n            <tr><td>VG 320<\/td><td>320<\/td><td>24.5<\/td><td>Heavy gears, worm<\/td><\/tr>\n            <tr><td>VG 460<\/td><td>460<\/td><td>31<\/td><td>Heavily loaded gears<\/td><\/tr>\n            <tr><td>VG 680<\/td><td>680<\/td><td>40<\/td><td>Very heavy gears<\/td><\/tr>\n            <tr><td>VG 1000<\/td><td>1000<\/td><td>52<\/td><td>Open gears<\/td><\/tr>\n            <tr><td>VG 1500<\/td><td>1500<\/td><td>68<\/td><td>Open gears, wire ropes<\/td><\/tr>\n        <\/tbody><\/table>\n        <div class=\"vc-info-box\"><p><strong>\ud83d\udca1 Optimal range:<\/strong> Most bearings and gears operate best at 13\u2013100 cSt. Below 13 cSt boundary lubrication risk; above 100 cSt excessive churning.<\/p><\/div>\n    <\/div><\/div>\n<\/div>\n\n<div class=\"vc-section\" id=\"vc-sec-related\"><button type=\"button\" class=\"vc-section-toggle\" aria-expanded=\"false\"><span class=\"vc-section-toggle-text\"><span class=\"vc-section-icon\">\ud83d\udd17<\/span><span class=\"vc-section-title\">Related Calculators<\/span><\/span><svg class=\"vc-section-chevron\" viewbox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\"><path d=\"M6 9l6 6 6-6\"\/><\/svg><\/button><div class=\"vc-section-body\"><div class=\"vc-section-inner\"><div class=\"vc-related\"><a class=\"vc-related-link\" href=\"\/calculators\/gear-oil-quantity\/\">Gear Oil Quantity<\/a><a class=\"vc-related-link\" href=\"\/calculators\/oil-change-interval\/\">Oil Change Interval<\/a><a class=\"vc-related-link\" href=\"\/calculators\/density-mass-volume\/\">Density Calculator<\/a><\/div><\/div><\/div><\/div>\n\n<div class=\"vc-section\" id=\"vc-sec-faq\"><button type=\"button\" class=\"vc-section-toggle\" aria-expanded=\"false\"><span class=\"vc-section-toggle-text\"><span class=\"vc-section-icon\">\u2753<\/span><span class=\"vc-section-title\">Frequently Asked Questions<\/span><\/span><svg class=\"vc-section-chevron\" viewbox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\"><path d=\"M6 9l6 6 6-6\"\/><\/svg><\/button><div class=\"vc-section-body\"><div class=\"vc-section-inner\"><div class=\"vc-faq-list\" id=\"vc-faq-list\"><\/div><\/div><\/div><\/div>\n\n<div class=\"vc-promo\"><div class=\"vc-promo-text\"><strong>Vibromera<\/strong> \u2014 Portable Balancing &amp; Vibration Analysis. 50+ countries.<\/div><a class=\"vc-promo-link\" href=\"https:\/\/vibromera.eu\/\" target=\"_blank\" rel=\"noopener\">Learn More<\/a><\/div>\n<footer class=\"vc-footer\"><p>\u00a9 2024\u20132025 <a href=\"https:\/\/vibromera.eu\/\">Vibromera<\/a><\/p><div class=\"vc-footer-links\"><a href=\"\/calculators\/engineering-calculators\/\">All Calculators<\/a><a href=\"https:\/\/vibromera.eu\/contacts\/\">Contact<\/a><\/div><\/footer>\n<\/div>\n\n<script src=\"https:\/\/cdn.jsdelivr.net\/npm\/katex@0.16.11\/dist\/katex.min.js\"><\/script>\n<script>\n(function(){\n    'use strict';var SLUG='oil-viscosity-temperature';function $(id){return document.getElementById(id)}\n    var VG_V100={10:2.6,15:3.3,22:4.4,32:5.4,46:6.8,68:8.7,100:11.4,150:15,220:19,320:24.5,460:31,680:40,1000:52,1500:68};\n\n    function walther(v40,v100,tC){\n        var T1=273.15+40,T2=273.15+100,T3=273.15+tC;\n        var W1=Math.log10(Math.log10(v40+0.7));var W2=Math.log10(Math.log10(v100+0.7));\n        var logT1=Math.log10(T1),logT2=Math.log10(T2);\n        var B=(W1-W2)\/(logT2-logT1);var A=W1+B*logT1;\n        var W3=A-B*Math.log10(T3);var v=Math.pow(10,Math.pow(10,W3))-0.7;\n        return{v:v,A:A,B:B};\n    }\n\n    function approxVI(v40,v100){\n        \/\/ ISO 2909:2002 \/ ASTM D2270: Table 1 subset (linear interpolation) for v100 = 2-70 cSt,\n        \/\/ official equations above 70 cSt; Procedure A for VI<=100, Procedure B for VI>100.\n        if(!(v40>0)||!(v100>=2)||v40<=v100)return NaN;\n        var L,H;\n        if(v100<=70){\n            var T=[[2,7.994,6.394],[2.5,11.45,9.063],[3,15.49,12.15],[3.5,20.09,15.66],[4,25.32,19.56],[4.5,31.96,23.81],[5,40.23,28.49],[5.5,49.09,33.34],[6,57.97,38.19],[6.5,67.12,43.18],[7,78.00,48.57],[7.5,88.85,53.98],[8,100.0,59.60],[8.5,111.5,65.32],[9,123.3,71.10],[9.5,135.3,76.91],[10,147.7,82.87],[11,173.9,95.19],[12,201.9,108.0],[13,231.9,121.5],[14,263.3,135.4],[15,296.5,149.7],[16,331.9,164.6],[17,369.4,180.2],[18,408.6,196.2],[19,449.9,212.7],[20,493.2,229.5],[22,585.2,264.9],[24,683.9,301.8],[26,790.4,340.5],[28,904.1,380.6],[30,1024,421.7],[35,1356,532.5],[40,1730,651.8],[45,2152,780.9],[50,2618,919.6],[55,3126,1066],[60,3676,1222],[65,4268,1386],[70,4905,1558]];\n            var i=1;while(i<T.length-1&&T[i][0]<v100)i++;\n            var a=T[i-1],b=T[i],f=(v100-a[0])\/(b[0]-a[0]);\n            L=a[1]+f*(b[1]-a[1]);H=a[2]+f*(b[2]-a[2]);\n        }else{\n            L=0.8353*v100*v100+14.67*v100-216;\n            H=0.1684*v100*v100+11.85*v100-97;\n        }\n        if(isNaN(L)||isNaN(H)||L<=H)return NaN;\n        if(v40>=H)return Math.round(((L-v40)\/(L-H))*100); \/\/ Procedure A (VI <= 100)\n        var n=(Math.log10(H)-Math.log10(v40))\/Math.log10(v100); \/\/ Procedure B (VI > 100)\n        return Math.round((Math.pow(10,n)-1)\/0.00715+100);\n    }\n\n    function estimatePourPoint(v40,vi){\n        \/\/ Very rough: pour point correlates with viscosity and VI\n        var base=-15-vi*0.05;\n        if(v40>200) base+=5;\n        if(v40>500) base+=5;\n        return Math.round(base\/3)*3; \/\/ round to nearest 3\n    }\n\n    function drawWaltherChart(v40,v100,tgt,vt,cA,cB){\n        var el=$('vc-viz-svg');if(!el)return;\n        var W=600,H=350,ml=65,mr=25,mt=25,mb=45,pw=W-ml-mr,ph=H-mt-mb;\n        var tMin=0,tMax=120,vMin=2,vMax=1000;\n        var ltMin=Math.log10(tMin+273.15),ltMax=Math.log10(tMax+273.15);\n        var wMin=Math.log10(Math.log10(vMin+.7)),wMax=Math.log10(Math.log10(vMax+.7));\n        function xP(t){return ml+(Math.log10(t+273.15)-ltMin)\/(ltMax-ltMin)*pw}\n        function yP(v){var w=Math.log10(Math.log10(Math.max(v,.8)+.7));return mt+ph-(w-wMin)\/(wMax-wMin)*ph}\n        function viscAt(t){var w=cA-cB*Math.log10(t+273.15);var r=Math.pow(10,Math.pow(10,w))-.7;return r>0?r:.5}\n        var o='<svg viewBox=\"0 0 600 350\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\">';\n        o+='<rect x=\"'+xP(40)+'\" y=\"'+mt+'\" width=\"'+(xP(60)-xP(40))+'\" height=\"'+ph+'\" fill=\"var(--vc-green)\" opacity=\"0.06\"\/>';\n        o+='<text x=\"'+((xP(40)+xP(60))\/2)+'\" y=\"'+(mt+13)+'\" text-anchor=\"middle\" font-family=\"var(--vc-mono)\" font-size=\"8\" fill=\"var(--vc-green)\" opacity=\"0.7\">Optimal 40\\u201360\\u00b0C<\/text>';\n        var vHi=v40*1.1,vLo=v40*.9,byH=yP(vHi),byL=yP(vLo);\n        if(byL>mt&&byH<mt+ph){o+='<rect x=\"'+ml+'\" y=\"'+byH+'\" width=\"'+pw+'\" height=\"'+(byL-byH)+'\" fill=\"var(--vc-blue)\" opacity=\"0.06\"\/>';\n            o+='<text x=\"'+(ml+pw-2)+'\" y=\"'+(byH+10)+'\" text-anchor=\"end\" font-family=\"var(--vc-mono)\" font-size=\"8\" fill=\"var(--vc-blue)\" opacity=\"0.6\">ISO VG \\u00b110%<\/text>';}\n        var gc='#e8e4dd',tT=[0,20,40,60,80,100,120];\n        for(var i=0;i<tT.length;i++){var tx=xP(tT[i]);\n            o+='<line x1=\"'+tx+'\" y1=\"'+mt+'\" x2=\"'+tx+'\" y2=\"'+(mt+ph)+'\" stroke=\"'+gc+'\" stroke-width=\"0.5\"\/>';\n            o+='<text x=\"'+tx+'\" y=\"'+(H-8)+'\" text-anchor=\"middle\" font-family=\"var(--vc-mono)\" font-size=\"10\" fill=\"#8a857e\">'+tT[i]+'\\u00b0C<\/text>';}\n        var vT=[2,5,10,20,50,100,200,500,1000];\n        for(var j=0;j<vT.length;j++){var vy=yP(vT[j]);\n            if(vy>=mt&&vy<=mt+ph){o+='<line x1=\"'+ml+'\" y1=\"'+vy+'\" x2=\"'+(ml+pw)+'\" y2=\"'+vy+'\" stroke=\"'+gc+'\" stroke-width=\"0.5\"\/>';\n                o+='<text x=\"'+(ml-5)+'\" y=\"'+(vy+4)+'\" text-anchor=\"end\" font-family=\"var(--vc-mono)\" font-size=\"10\" fill=\"#8a857e\">'+vT[j]+'<\/text>';}}\n        var pts='';for(var k=0;k<=100;k++){var tk=tMin+(tMax-tMin)*k\/100,vk=viscAt(tk);\n            if(vk<.8)vk=.8;if(vk>2000)vk=2000;pts+=xP(tk).toFixed(1)+','+yP(vk).toFixed(1)+' ';}\n        o+='<polyline points=\"'+pts+'\" fill=\"none\" stroke=\"var(--vc-accent)\" stroke-width=\"2.5\"\/>';\n        o+='<circle cx=\"'+xP(40)+'\" cy=\"'+yP(v40)+'\" r=\"5\" fill=\"var(--vc-ink)\" stroke=\"#fff\" stroke-width=\"1.5\"\/>';\n        o+='<text x=\"'+(xP(40)+8)+'\" y=\"'+(yP(v40)-7)+'\" font-family=\"var(--vc-mono)\" font-size=\"9\" fill=\"var(--vc-ink-secondary)\">\\u03bd\\u2084\\u2080='+v40+'<\/text>';\n        o+='<circle cx=\"'+xP(100)+'\" cy=\"'+yP(v100)+'\" r=\"5\" fill=\"var(--vc-ink)\" stroke=\"#fff\" stroke-width=\"1.5\"\/>';\n        o+='<text x=\"'+(xP(100)+8)+'\" y=\"'+(yP(v100)-7)+'\" font-family=\"var(--vc-mono)\" font-size=\"9\" fill=\"var(--vc-ink-secondary)\">\\u03bd\\u2081\\u2080\\u2080='+v100+'<\/text>';\n        if(vt>0&&isFinite(vt)){\n            o+='<line x1=\"'+ml+'\" y1=\"'+yP(vt).toFixed(1)+'\" x2=\"'+xP(tgt).toFixed(1)+'\" y2=\"'+yP(vt).toFixed(1)+'\" stroke=\"var(--vc-accent)\" stroke-width=\"1\" stroke-dasharray=\"4,3\" opacity=\"0.5\"\/>';\n            o+='<circle cx=\"'+xP(tgt)+'\" cy=\"'+yP(vt)+'\" r=\"7\" fill=\"var(--vc-accent)\" stroke=\"#fff\" stroke-width=\"2\"\/>';\n            o+='<text x=\"'+(xP(tgt)+10)+'\" y=\"'+(yP(vt)+4)+'\" font-family=\"var(--vc-font)\" font-size=\"10\" font-weight=\"600\" fill=\"var(--vc-accent)\">'+vt.toFixed(1)+' cSt @ '+tgt+'\\u00b0C<\/text>';}\n        o+='<line x1=\"'+ml+'\" y1=\"'+mt+'\" x2=\"'+ml+'\" y2=\"'+(mt+ph)+'\" stroke=\"var(--vc-ink)\" stroke-width=\"1.5\"\/>';\n        o+='<line x1=\"'+ml+'\" y1=\"'+(mt+ph)+'\" x2=\"'+(ml+pw)+'\" y2=\"'+(mt+ph)+'\" stroke=\"var(--vc-ink)\" stroke-width=\"1.5\"\/>';\n        o+='<text x=\"'+(ml+pw\/2)+'\" y=\"'+(H-1)+'\" text-anchor=\"middle\" font-family=\"var(--vc-font)\" font-size=\"10\" fill=\"var(--vc-ink-secondary)\">Temperature<\/text>';\n        o+='<text x=\"14\" y=\"'+(mt+ph\/2)+'\" text-anchor=\"middle\" font-family=\"var(--vc-font)\" font-size=\"10\" fill=\"var(--vc-ink-secondary)\" transform=\"rotate(-90,14,'+(mt+ph\/2)+')\">\\u03bd Viscosity (cSt)<\/text>';\n        o+='<\/svg>';el.innerHTML=o;}\n\n    function calculate(){\n        var vgVal=$('vc-vg').value;\n        var v40=vgVal?parseFloat(vgVal):parseFloat($('vc-v40').value);\n        var v100=vgVal?VG_V100[parseInt(vgVal)]||parseFloat($('vc-v100').value):parseFloat($('vc-v100').value);\n        var tgt=parseFloat($('vc-tgt').value);\n        if(vgVal){$('vc-v40').value=v40;$('vc-v100').value=v100}\n        if(isNaN(v40)||isNaN(v100)||isNaN(tgt)||v40<1||v100<0.5){$('vc-results').classList.remove('vc-visible');return}\n\n        var r=walther(v40,v100,tgt);if(isNaN(r.v)||r.v<0)r.v=0;\n        var vi=approxVI(v40,v100);\n        var pp=estimatePourPoint(v40,isNaN(vi)?90:vi);\n\n        \/\/ Operating range check\n        var rangeMsg;\n        if(r.v<5) rangeMsg='<span style=\"color:var(--vc-accent)\">\u26a0\ufe0f VERY LOW \u2014 Boundary lubrication risk. Consider thicker oil.<\/span>';\n        else if(r.v<13) rangeMsg='<span style=\"color:var(--vc-yellow)\">Marginal \u2014 Below optimal range (13\u2013100 cSt). Monitor wear.<\/span>';\n        else if(r.v<=100) rangeMsg='<span style=\"color:var(--vc-green)\">\u2713 OPTIMAL \u2014 Within 13\u2013100 cSt operating range.<\/span>';\n        else if(r.v<=500) rangeMsg='<span style=\"color:var(--vc-yellow)\">High \u2014 Above optimal. May cause churning losses.<\/span>';\n        else rangeMsg='<span style=\"color:var(--vc-accent)\">\u26a0\ufe0f VERY HIGH \u2014 Excessive viscosity. Check startup conditions.<\/span>';\n\n        \/\/ Dynamic viscosity (approx \u03c1 = 0.87 for typical oil)\n        var dynVisc=r.v*0.87;\n\n        $('vc-r-visc').innerHTML=(r.v>1000?r.v.toFixed(0):r.v.toFixed(2))+' <span class=\"vc-rcard-unit\">cSt (mm\u00b2\/s) at '+tgt+'\u00b0C<\/span>';\n        $('vc-r-vi').textContent=isNaN(vi)?'\u2014':'\u2248 '+vi+(vi>=120?' (excellent)':vi>=95?' (good)':vi>=80?' (fair)':' (low)');\n        $('vc-r-range').innerHTML=rangeMsg;\n        $('vc-r-A').textContent=r.A.toFixed(5);\n        $('vc-r-B').textContent=r.B.toFixed(5);\n        $('vc-r-ref').innerHTML=v40.toFixed(1)+' \/ '+v100.toFixed(1)+' <span class=\"vc-rcard-unit\">cSt (40\u00b0C \/ 100\u00b0C)<\/span>';\n        $('vc-r-pour').innerHTML='\u2248 '+pp+' <span class=\"vc-rcard-unit\">\u00b0C (estimated)<\/span>';\n        $('vc-r-dyn').innerHTML=dynVisc.toFixed(1)+' <span class=\"vc-rcard-unit\">mPa\u00b7s (at \u03c1\u22480.87)<\/span>';\n\n        $('vc-results').classList.add('vc-visible');\n        drawWaltherChart(v40,v100,tgt,r.v,r.A,r.B);\n\n        try{var u=new URLSearchParams();u.set('v40',v40);u.set('v100',v100);u.set('t',tgt);history.replaceState(null,'','?'+u.toString())}catch(e){}\n        saveHistory({v40:v40,v100:v100,t:tgt,vt:+r.v.toFixed(2),vi:vi,_summary:'\u03bd('+tgt+'\u00b0C)='+r.v.toFixed(1)+' cSt, VI\u2248'+(isNaN(vi)?'\u2014':vi)});\n    }\n\n    function saveHistory(e){var k='vc_history_'+SLUG;var a=[];try{a=JSON.parse(localStorage.getItem(k))||[]}catch(x){}e._ts=new Date().toISOString();a.unshift(e);if(a.length>10)a=a.slice(0,10);try{localStorage.setItem(k,JSON.stringify(a))}catch(x){}}\n    function loadURL(){try{var p=new URLSearchParams(location.search);if(p.has('v40')){$('vc-v40').value=p.get('v40');$('vc-v100').value=p.get('v100');$('vc-tgt').value=p.get('t');$('vc-vg').value=''}}catch(e){}}\n\n    $('vc-form').addEventListener('input',function(e){if(e.target.id!=='vc-vg')$('vc-vg').value='';calculate()});\n    $('vc-form').addEventListener('change',calculate);\n    document.querySelectorAll('.vc-preset-btn').forEach(function(b){b.addEventListener('click',function(e){e.preventDefault();$('vc-v40').value=this.getAttribute('data-v40');$('vc-v100').value=this.getAttribute('data-v100');$('vc-tgt').value=this.getAttribute('data-t');$('vc-vg').value=this.getAttribute('data-vg');calculate()})});\n    $('vc-copy-btn').addEventListener('click',function(){var t='Oil Viscosity\u2013Temperature\\n\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\\n'+$('vc-r-visc').textContent+'\\nVI: '+$('vc-r-vi').textContent+'\\nA='+$('vc-r-A').textContent+', B='+$('vc-r-B').textContent+'\\nPour point: '+$('vc-r-pour').textContent+'\\n\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\\nvibromera.eu';if(navigator.clipboard)navigator.clipboard.writeText(t)});\n    document.querySelectorAll('.vc-section-toggle').forEach(function(btn){btn.addEventListener('click',function(){this.closest('.vc-section').classList.toggle('vc-open')})});\n\n    var faqData=[\n        {q:'What is the Walther equation and how accurate is it?',a:'<p>The Walther equation (ASTM D341): log log(\u03bd+0.7) = A \u2212 B \u00d7 log(T). It produces a straight line on ASTM viscosity-temperature chart paper.<\/p><p>Very accurate for mineral oils from \u221220\u00b0C to 150\u00b0C. Less accurate for heavily additized synthetics, near pour point, or near flash point.<\/p>'},\n        {q:'What is Viscosity Index (VI) and what values are good?',a:'<p>VI indicates how much viscosity changes with temperature. Higher = more stable.<\/p><ul><li>VI < 80: Low (naphthenic base)<\/li><li>VI 80\u2013100: Normal mineral oil<\/li><li>VI 100\u2013120: Good (HVI or semi-synthetic)<\/li><li>VI 120\u2013160: Very good (PAO synthetic)<\/li><li>VI > 160: Excellent (multigrade, VI-improved)<\/li><\/ul>'},\n        {q:'What is the optimal operating viscosity range?',a:'<p>For most bearings and gears: <strong>13\u2013100 cSt<\/strong> at operating temperature.<\/p><ul><li>Below 13 cSt: boundary lubrication risk, increased wear<\/li><li>13\u201330 cSt: hydrodynamic bearings, high-speed gears<\/li><li>30\u2013100 cSt: general industrial gears and bearings<\/li><li>Above 100 cSt: may cause churning losses, high startup torque<\/li><\/ul>'},\n        {q:'How do I convert cSt to other units?',a:'<p>Kinematic viscosity: 1 cSt = 1 mm\u00b2\/s exactly.<\/p><p>Dynamic viscosity: \u03b7 = \u03bd \u00d7 \u03c1. Units: mPa\u00b7s = cSt \u00d7 g\/cm\u00b3. For typical oil at 15\u00b0C: \u03c1 \u2248 0.87 g\/cm\u00b3, so 100 cSt = 87 mPa\u00b7s.<\/p><p>SUS (Saybolt): roughly SUS \u2248 4.6 \u00d7 cSt (for cSt > 50).<\/p>'},\n        {q:'What is pour point and why does it matter?',a:'<p>Pour point is the lowest temperature at which oil still flows. Below pour point, wax crystallization makes the oil too thick to pump. It matters for cold-start conditions, outdoor equipment, and Arctic applications.<\/p><p>Mineral oils: typically \u221215 to \u221230\u00b0C. PAO synthetics: \u221240 to \u221260\u00b0C.<\/p>'}\n    ];\n    var fl=$('vc-faq-list');faqData.forEach(function(f){fl.innerHTML+='<div class=\"vc-faq-item\"><button type=\"button\" class=\"vc-faq-q\"><span>'+f.q+'<\/span><svg class=\"vc-faq-chevron\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\"><path d=\"M6 9l6 6 6-6\"\/><\/svg><\/button><div class=\"vc-faq-a\"><div class=\"vc-faq-a-inner\">'+f.a+'<\/div><\/div><\/div>'});\n    fl.addEventListener('click',function(e){var b=e.target.closest('.vc-faq-q');if(!b)return;b.closest('.vc-faq-item').classList.toggle('vc-open')});\n\n    function renderFormulas(){try{\n        katex.render('\\\\log\\\\!\\\\log(\\\\nu + 0.7) = A - B \\\\cdot \\\\log(T_K)',$('vc-katex-1'),{displayMode:true,throwOnError:false});\n        katex.render('VI = \\\\frac{L - \\\\nu_{40}}{L - H} \\\\times 100',$('vc-katex-2'),{displayMode:true,throwOnError:false});\n    }catch(e){}}\n    function init(){loadURL();renderFormulas();calculate()}\n    if(document.readyState==='loading')document.addEventListener('DOMContentLoaded',init);else init();\n})();\n<\/script>\n","protected":false},"excerpt":{"rendered":"<p>Libreng calculator ng viscosity ng langis gamit ang Walther (ASTM D341) na equation. Kalkulahin ang kinematic viscosity sa anumang temperatura. Viscosity Index ayon sa ASTM D2270. Mga klase ng ISO VG. Pagtatantya ng pour point.<\/p>","protected":false},"featured_media":0,"template":"","meta":{"ai_generated_summary":"","footnotes":""},"categories":[],"tags":[],"class_list":["post-100178","calculator","type-calculator","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/vibromera.eu\/tl\/wp-json\/wp\/v2\/calculator\/100178","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/vibromera.eu\/tl\/wp-json\/wp\/v2\/calculator"}],"about":[{"href":"https:\/\/vibromera.eu\/tl\/wp-json\/wp\/v2\/types\/calculator"}],"version-history":[{"count":3,"href":"https:\/\/vibromera.eu\/tl\/wp-json\/wp\/v2\/calculator\/100178\/revisions"}],"predecessor-version":[{"id":102129,"href":"https:\/\/vibromera.eu\/tl\/wp-json\/wp\/v2\/calculator\/100178\/revisions\/102129"}],"wp:attachment":[{"href":"https:\/\/vibromera.eu\/tl\/wp-json\/wp\/v2\/media?parent=100178"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/vibromera.eu\/tl\/wp-json\/wp\/v2\/categories?post=100178"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/vibromera.eu\/tl\/wp-json\/wp\/v2\/tags?post=100178"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}