How mass conversion works
CalcOS relates every supported mass unit to the kilogram, the SI base unit of mass. Metric units use exact powers of ten. International customary units use the exact definition of the avoirdupois pound.
This single canonical pathway prevents kilogram-to-pound and pound-to-kilogram pages from drifting through separately rounded multipliers.
Supported mass units
| Unit | Relationship to kilogram | Definition status |
|---|---|---|
| milligram (mg) | 0.000001 kg | exact |
| gram (g) | 0.001 kg | exact |
| kilogram (kg) | 1 kg | SI base unit |
| ounce (oz) | 0.028349523125 kg | exact |
| pound (lb) | 0.45359237 kg | exact |
Why the page says “Weight and Mass”
People commonly search for weight conversions when they mean kilograms or pounds. Scientifically, those units describe mass. Weight is a force that changes with gravitational acceleration. CalcOS retains the familiar label for discoverability while explaining the quantity accurately.
Choose the correct ounce
This converter uses the avoirdupois ounce for common goods and body mass. A troy ounce is heavier and is used mainly for precious metals. A fluid ounce measures volume, not mass. Those units must never be treated as interchangeable.
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Authoritative references: BIPM SI Brochure and NIST Handbook 44, Appendix C.