The kilogram is the primary unit of mass in the International System of Units (SI).
Definition & Scientific Metrology
The kilogram (symbol: kg) is the base unit of mass in the metric system. Since 2019, it is defined in terms of the Planck constant (h = 6.62607015×10⁻³⁴ J·s), providing an invariant physical definition.
1 kgOrigins & Historical Evolution
Originally created in 1795 in France as the mass of one liter of pure water at 4°C, it was later embodied by the International Prototype of the Kilogram (IPK) cylinder until the 2019 SI redefinition.
1 Kilogram in Other Mass Units
Direct standard conversion equivalents for 1 kg:
| Target Unit | Equivalent Value | Multiplier Equation |
|---|---|---|
| Grams (g) | 1,000 | 1 kg × 1000 |
| Milligrams (mg) | 1,000,000 | 1 kg × 1000000 |
| Pounds (lbs) | 2.205 | 1 kg × 2.20462262 |
| Ounces (oz) | 35.274 | 1 kg × 35.27396195 |
| Stones (st) | 0.157 | 1 kg × 0.157473044 |
| Metric Tons (t) | 0.001 | 1 kg × 0.001 |
| US Tons | 0.001 | 1 kg × 0.00110231 |
| Micrograms (µg) | 1,000,000,000 | 1 kg × 1000000000 |
Common Real-World Applications
- Human body weight in most international countries
- Grocery and bulk food weighing worldwide
- Aviation cargo, luggage limits, and shipping tariffs
- Engineering and physics calculations
Interesting Metrology Facts
The kilogram is the only SI base unit that has an SI prefix (kilo-) in its official name.
1 liter of pure water at standard temperature and pressure weighs exactly 1 kilogram.
Measurement Standards & Accuracy
Standard MultipliersFactors based on the 1959 International Yard and Pound Agreement and NIST SP 811.
- BIPM International Metrology Treaty
- NIST Guide for SI Units
- ISO 80000-4 Quantities and Units — Mass
Related Tools & Resources for Kilogram
Discover calculation widgets, unit comparisons, and printable lookup sheets for kg: