Every converter, chart and answer on OneEquals is calculated from exact, published definitions. Nothing is copied from other websites.
The definitions we use
- Length: 1 inch = 2.54 cm exactly, 1 foot = 0.3048 m, 1 yard = 0.9144 m, 1 mile = 1,609.344 m (international yard and pound agreement, 1959).
- Weight: 1 pound = 0.45359237 kg exactly, 1 ounce = 1/16 lb = 28.349523125 g, 1 troy ounce = 31.1034768 g.
- Volume: 1 US gallon = 231 cubic inches = 3.785411784 L; 1 US fluid ounce = 1/128 US gallon; 1 imperial gallon = 4.54609 L.
- Temperature: °F = °C × 9/5 + 32 and K = °C + 273.15.
- Data: decimal units (1 GB = 1,000,000,000 bytes) and binary units (1 GiB = 1,073,741,824 bytes) are kept separate.
- Ring sizes: US circumference = 2.55 × size + 36.5 mm; EU/ISO size = inside circumference in mm; UK letters per BS 6820.
- Shoe sizes: there is no official worldwide standard, and brands differ. Our tables follow widely used retailer conversions and include foot length so you can check against your own measurement.
Sources
- NIST Handbook 44, Appendix C: General Tables of Units of Measurement
- NIST Special Publication 811: Guide for the Use of the International System of Units
- BIPM: The International System of Units (SI Brochure)
Rounding
Factors are stored to full precision. Results are rounded only for display: the converter lets you choose the number of decimals, and charts round to a sensible precision for each unit. Exact factors are shown in each page’s “How to convert” section.
Corrections
If you spot an error, email hello@oneequals.com. We check and correct reported issues.