Free Engineering Tool
Viscosity Converter
Cross-reference between ISO VG, SAE crankcase, SAE gear, and AGMA viscosity grades. Also convert between cSt, cP, and SUS units.
Results
ISO VG / SAE / AGMA Cross-Reference
Approximate equivalence between viscosity grading systems. These are not exact conversions — each system uses different measurement conditions.
| ISO VG | cSt Range (40 °C) | SAE Crankcase | SAE Gear | AGMA |
|---|
Unit Conversion Formulas
Where: 1 cP = 1 mPa·s, and 1 cSt = 1 mm²/s. Oil density is typically 0.85–0.90 g/cm³ (850–900 kg/m³); for an exact conversion use the density at the same temperature as the kinematic viscosity (density at 40 °C is about 1.5 % lower than at 15 °C).
The Saybolt Universal Seconds (SUS) approximation is valid for viscosities above ~50 cSt. For lower viscosities, a more complex formula is needed, but the above gives reasonable results for most industrial oils.
About the Grading Systems
- ISO VG (ISO 3448) — Industrial lubricants; 18 grades VG 2 to VG 1500; kinematic viscosity at 40 °C ± 10%.
- SAE Crankcase (SAE J300) — Automotive engine oils; grades like 10W, 20, 30, 40, 50; measured at 100 °C.
- SAE Gear (SAE J306) — Automotive gear oils; grades like 75W, 80W-90, 140, 250; measured at 100 °C.
- AGMA (AGMA 9005) — Industrial gear lubricants; grades 1 through 8A; aligned with ISO VG.
⚠️ Important: Cross-references are approximate. ISO VG measures at 40 °C while SAE measures at 100 °C. Always verify with the specific oil product data sheet for exact viscosity values at your operating temperature.
ISO VG (ISO 3448) classifies industrial lubricants by kinematic viscosity at 40 °C. SAE grades classify automotive oils at 100 °C (SAE J300 for engine oils, SAE J306 for gear oils).
Because they measure at different temperatures, there is no exact conversion — only approximate equivalence. For example, ISO VG 68 ≈ SAE 20W-20 for crankcase oil.
Different industries developed classification systems independently:
- ISO VG — International standard for industrial lubricants
- SAE J300 — Automotive engine oils (Society of Automotive Engineers)
- SAE J306 — Automotive gear oils
- AGMA 9005 — Industrial gear lubricants (American Gear Manufacturers Association)
Each system is optimized for its specific application and operating conditions.
AGMA (American Gear Manufacturers Association) defines lubricant specifications for industrial gears per AGMA 9005. AGMA grades 1 through 8A cover the range from ISO VG 32 to VG 1000.
AGMA grades are commonly used in North America for specifying gear lubricants, especially for enclosed industrial gearboxes.
cSt (centistokes) = kinematic viscosity (mm²/s). It measures how a fluid flows under gravity.
cP (centipoise) = dynamic viscosity (mPa·s). It measures resistance to flow under applied force.
Conversion: cP = cSt × density (g/cm³). For typical mineral oil (~0.87 g/cm³), dynamic viscosity is about 87% of kinematic viscosity.
Multigrade SAE oil ratings contain two numbers:
- First number + W (e.g. 10W) — Cold-start viscosity grade (W = Winter). Lower number = better cold flow.
- Second number (e.g. 30) — Operating temperature viscosity grade at 100 °C.
A 10W-30 oil flows like a 10W at cold temperatures (−25 °C) but maintains the film strength of a 30-weight oil at 100 °C. This is achieved using viscosity index improver additives.
The procedures described on this page were developed and field-tested by the Vibromera team using the Balanset-1A, a portable dual-channel balancer and vibration analyzer for on-site rotor balancing.
Professional field balancing instruments and software. Used in 50+ countries for rotating machinery maintenance.
Nikolai Shelkovenko
Nikolai Shelkovenko is a vibration analysis engineer and the founder and CEO of Vibromera. For more than 15 years he has balanced rotating equipment in the field rather than on a test bench: mulchers, industrial fans, crushers, centrifuges, shafts and spindles. That work is what the Balanset instruments grew out of — they were designed as a tool a specialist can carry to the machine and use alone, on site, not as laboratory equipment. Vibromera was founded in 2017 and has been based in Porto, Portugal, since 2023. Development, assembly and support of the Balanset line all happen here. The flagship instrument is the Balanset-1A, a portable analyser for single- and two-plane balancing and for vibration diagnostics. Nikolai is personally involved in customer support, in working through difficult balancing cases and in the development of the software. He works with customers worldwide, in any language.
