Sources & References
Conversion factors are based on the following widely recognized standards and definitions. Where a unit has an exact legal definition, that exact value is used.
Primary standards
- International System of Units (SI) base and derived unit definitions from the BIPM (Bureau International des Poids et Mesures).
- The international yard and pound agreement of 1959: 1 yard = 0.9144 m, 1 pound = 0.45359237 kg (both exact).
- NIST (US National Institute of Standards and Technology) special publications on units and conversion factors.
- IEC 80000-13 for binary prefixes (kibibyte, mebibyte, gibibyte).
Selected exact definitions used
| Relationship | Value |
|---|---|
| 1 inch | 0.0254 m (exact) |
| 1 foot | 0.3048 m (exact) |
| 1 mile | 1609.344 m (exact) |
| 1 pound | 0.45359237 kg (exact) |
| 1 US gallon | 3.785411784 L (exact) |
| 1 Imperial gallon | 4.54609 L (exact) |
| 1 acre | 4046.8564224 m² (43,560 ft²) |
| Standard atmosphere | 101,325 Pa (exact) |
| 1 pound-force | 4.4482216152605 N |
| 1 calorie (thermochemical) | 4.184 J (exact) |
Approximate values
A few units depend on context and are marked as approximate in the tool. Average calendar month and year lengths use the Gregorian calendar (365.2425 days per year). Sea-level standard values are noted where relevant. These are labeled so you can apply a more precise figure when your application requires it.