What the conversions are based on
Inches, feet, miles and pounds have had exact metric definitions since the 1959 international agreement. This converter uses the definitions below and rounds only what it shows you.
| Unit | Definition |
|---|---|
| 1 inch (in) | 2.54 cm exactly |
| 1 foot (ft) | 30.48 cm = 12 in |
| 1 mile (mi) | 1.609344 km |
| 1 pound (lb) | 0.45359237 kg = 16 oz |
| 1 ounce (oz) | 28.349523125 g |
| 1 acre (ac) | 4,046.8564224 m² = 43,560 ft² |
| 1 US gallon | 3.785411784 L = 128 fl oz |
| 1 UK gallon | 4.54609 L |
| 1 US cup | 236.5882365 mL |
| 1 pyeong (평) | 400/121 m² ≈ 3.3058 m² |
| 1 don (돈) | 3.75 g |
Temperature uses a formula, not a ratio
The scales start from different zero points, so multiplying alone gives the wrong answer. Body temperature of 37 °C is 98.6 °F, and −40 is the same in both. Kelvin cannot go below 0 K (−273.15 °C).
Common conversions
| Value | Converted |
|---|---|
| 170 cm | 5.5774 ft |
| 1 mi | 1.6093 km |
| 1 kg | 2.2046 lb |
| 1 don | 3.75 g |
| 84 m² | 904.17 ft² |
| 84 m² | 25.41 pyeong |
| 1 gal | 3.7854 L |
| 37 °C | 98.6 °F |
Units that are easy to mix up
Gallons, pints and cups differ between countries: a US gallon is about 3.785 L and a UK gallon about 4.546 L, and a recipe “cup” can differ by country or cookbook. Ounces (weight) and fluid ounces (volume) are different units too. In Korea, homes are often described in pyeong; the pyeong ↔ m² converter also explains Korean floor-area terms.
FAQ
How many centimeters is an inch?
Exactly 2.54 cm. A foot is 12 inches, so 30.48 cm.
How do I convert Fahrenheit to Celsius?
Subtract 32 and multiply by 5/9. For example, 77 °F is (77 − 32) × 5 ÷ 9 = 25 °C.
How many pounds is a kilogram?
About 2.2046 pounds, because a pound is exactly 0.45359237 kg.
What is a “don” in Korea?
A traditional unit used for gold and jewelry: 1 don is 3.75 g. Pick “Don” under Weight to convert it.
Sources
- NIST Special Publication 811 — Conversion factors (Appendix B)
- NIST — Unit conversion
- BIPM — The International System of Units (SI)