Weight Converter

Identify mass versus force

BIPM identifies the kilogram (kg) as the SI base unit of mass. NIST distinguishes mass from gravitational weight as a force, whose SI unit is the newton (N). The site’s “weight” calculator re-expresses supplied mass quantities.

Converting a kilogram amount to pounds does not calculate a load’s force or structural capacity. Select a force converter only when the source quantity is already a force.

• Convert stated force quantities
• Check units and conventions

Choose decimal or avoirdupois mass units

1 kg = 1000 g; 1 g = 1000 mg; 1 mg = 1000 μg. BIPM’s decimal prefix multipliers and NIST’s mass guidance establish these subdivisions.

The avoirdupois pound is exactly 0.45359237 kg. There are 16 avoirdupois ounces per pound, so one ounce is 28.349523125 g. Stone is 14 avoirdupois pounds, or 6.35029318 kg. The full definitions precede display rounding.

• Kilograms to avoirdupois pounds
• Avoirdupois pounds to kilograms
• Avoirdupois ounces to grams
• Stone to avoirdupois pounds

Distinguish ounce quantities

A fluid ounce measures volume, whereas the avoirdupois ounce here measures mass. NIST Handbook 44 also identifies a separate troy-ounce convention. This mass unit inventory has no troy ounce; do not enter a troy quantity as though it were avoirdupois.

Volume-to-mass conversion needs substance information, not just a mass-unit factor. The cooking tools identify supported recipe-reference estimates and require independently verified density for mL-to-mass results. A fluid-ounce value cannot be converted to grams by this mass calculator alone.

• Convert volume quantities
• Check ingredient references and density availability

Name the short, long or metric ton

Short ton: 2000 avoirdupois pounds = 907.18474 kg. Long ton: 2240 avoirdupois pounds = 1016.0469088 kg, or 1016046.9088 g. Tonne (metric ton): 1000 kg. These are different definitions, so an unqualified “ton” needs its source convention checked.

NIST’s published factors may show fewer digits. The rounded long-ton value 1016047 g is not its exact definition; calculate with the full factor and then round the final display.

• Pounds to short tons
• Long tons to metric tonnes
• Metric tonnes to kilograms

Separate mass carat from gold purity

NIST’s metric carat is a mass unit of exactly 0.2 g = 200 mg. One gram is therefore 5 metric mass carats. FTC’s jewelry guidance describes gold karat ratings as purity information, which is a different quantity.

A conversion of a supplied mass to carats does not determine gold purity, jewelry price or gemstone dimensions. The ounce-to-carat converter uses avoirdupois ounces, not troy ounces.

• Grams to metric mass carats
• Avoirdupois ounces to metric mass carats

Use mental estimates with a stated error

The exact kilogram-to-pound ratio is 1 / 0.45359237. Decimal factors such as 2.20462262 are rounded representations. The ×2.2 shortcut is about 0.2096786% low, derived from (2.2 × 0.45359237 − 1) × 100.

For a hypothetical 70 kg amount, ×2.2 gives 154 lb; the definition-derived result is approximately 154.3235835294 lb. For a hypothetical 160 lb amount, ×0.45 gives 72 kg rather than 72.5747792 kg. The reverse shortcut is about 0.7919820% low, derived from (0.45 / 0.45359237 − 1) × 100.

The two shortcut errors differ. An estimate does not establish whether a supplied amount meets a limit or specification. Check the original actual measurement and the original requirement rather than treating the shortcut as a compliance test.

• Read the mental-conversion guide
• Re-express package quantities
• Re-express supplied fitness quantities

Preserve original measurement precision

Exact unit definitions do not establish the accuracy of a measured mass. Calculate from the definitions before rounding the display, and retain the precision justified by the source. The calculator uses floating-point arithmetic; extra decimal places do not improve the original measurement.

For 1 kg, the default four-decimal result is 2.2046 lb. The reference table displays 2.204622622 lb at ten significant digits. These are differently rounded displays of the same ratio.

• Sources, calculations and rounding

Sources and review

• BIPM: kilogram as the SI mass base unit
• NIST: modern kilogram, mass and weight-force distinction
• NIST footnote 22: exact avoirdupois pound factor
• NIST Handbook 44 Appendix C: ounce, stone, ton and troy relationships
• NIST Appendix B.8: metric carat and named mass factors
• NIST Chapter 5: tonne definition
• BIPM: decimal prefix multipliers
• FTC: gold karat ratings describe purity

Reviewed 2026-10-06. Calculated values are displayed to at most ten significant digits; extra digits do not establish measurement accuracy.