Mass Unit Converter
Convert a non-negative mass between SI units,avoirdupois units,troy ounce,grain,stone and explicitly identified short and long tons. Every customary unit is named to prevent ounce,pound and ton ambiguity.
Convert one mass value
Select the unit that actually accompanies the source value. Changing the unit selector reinterprets—not converts—the number already entered.
Definitions used by the calculator
| Единица | Exact kilograms used | Definition or identity |
|---|---|---|
| milligram (mg) | 0.000001kg | SI prefix relation |
| gram (g) | 0.001kg | SI prefix relation |
| kilogram (kg) | 1kg | SI base unit of mass |
| tonne (t) | 1000kg | metric ton |
| grain (gr) | 0.00006479891kg | 1/7000 avoirdupois pound |
| ounce avoirdupois (oz av) | 0.028349523125kg | 1/16 avoirdupois pound |
| pound avoirdupois (lb av) | 0.45359237kg | international pound |
| stone (st) | 6.35029318kg | 14 avoirdupois pounds |
| short ton | 907.18474kg | 2000 avoirdupois pounds |
| long ton | 1016.0469088kg | 2240 avoirdupois pounds |
| troy ounce (oz t) | 0.0311034768kg | 480 grains;not an avoirdupois or fluid ounce |
| carat (ct) | 0.0002kg | 200mg |
The calculation first converts the input to kilograms,then divides by each listed kilograms-per-unit factor. Display values are rounded to at most12 significant digits;the machine-readable result retains the JavaScript numerical value. Do not infer measurement uncertainty or additional significant figures from a unit conversion.
Sources and standards status
BIPM,The International System of Units (SI),9th edition (2019),updated2026 is the current SI reference. NIST SP811 Appendix B.8 lists conversion factors for grain,avoirdupois and troy ounce,long ton,short ton and tonne;NIST’s footnotes identify the international avoirdupois pound as exactly0.45359237kg.
NIST’s mass guidance distinguishes mass from weight-force and states that the SI unit of weight in science and technology is the newton. Standard gravity gn=9.80665m/s² is an exact conventional value only when expressly selected;local gravity varies.
Balancing terminology correction
The former FAQ cited “ISO1940” as though it were current and described g·mm/kg as permissible residual unbalance. ISO’s official lifecycle records show ISO1940-1:2003 is withdrawn and revised by ISO21940-11:2016,which remains published,has Amendment1:2022 and was at systematic-review stage90.20 when checked in July2026. Mass×length (for example g·mm) and mass×length per rotor mass (for example g·mm/kg) are different quantities;this mass-only converter calculates neither an unbalance tolerance nor acceptance. Exact normative clauses and project criteria require the controlled standard.
What was corrected
The former title and introduction called kg,lb and oz both mass and weight units even though the calculator produced no force. It also used the bare symbols “lb” and “oz”,pre-filled a result,accepted negative masses and numeric prefixes through parseFloat,and did not disclose display rounding. The replacement is explicitly a mass converter,uses complete-number validation,starts blank and labels avoirdupois,troy,short-ton and long-ton systems.
Unsourced object-mass examples and steel “weight” estimates were removed because actual mass depends on dimensions,density,tolerances,configuration and rated container data. The exact unit definitions remain;engineering estimates belong in documented geometry/material calculators.
