What the unit converter does
The converter handles the everyday unit categories — length, weight, volume, temperature and speed — between metric and imperial/US customary systems. Pick a category, enter a value and choose the units on each side; the result updates as you type. It runs in your browser and covers the conversions that come up in recipes, travel, DIY, shipping and school work.
Exact conversion factors
| From | To | Multiply by |
|---|---|---|
| Inches | Centimetres | 2.54 (exact) |
| Feet | Metres | 0.3048 (exact) |
| Miles | Kilometres | 1.609344 (exact) |
| Pounds | Kilograms | 0.45359237 (exact) |
| Ounces | Grams | 28.349523 |
| US gallons | Litres | 3.785412 |
| US fluid ounces | Millilitres | 29.5735 |
| US cups | Millilitres | 236.588 (240 in recipes) |
| Knots | km/h | 1.852 (exact) |
| mph | km/h | 1.609344 (exact) |
Since 1959 the inch, foot, mile and pound have been defined in terms of metric units, so those factors are exact by definition rather than measured approximations.
Temperature is different
Temperature scales have different zero points, so they convert by a formula rather than a multiplier — you cannot say “double the Celsius”.
°F = °C × 9/5 + 32 °C = (°F − 32) × 5/9 K = °C + 273.15
0 °C = 32 °F (water freezes)
20 °C = 68 °F (room temperature)
37 °C = 98.6 °F (body temperature)
100 °C = 212 °F (water boils at sea level)
−40 °C = −40 °F (the scales cross)A quick mental estimate for Celsius to Fahrenheit: double it and add 30 (20 °C → 70 °F, true value 68). For oven temperatures, 180 °C ≈ 350 °F and 200 °C ≈ 400 °F.
Traps in the imperial system
- US vs UK gallons and pints. A US gallon is 3.785 L; an imperial (UK) gallon is 4.546 L. A US pint is 473 mL; a UK pint is 568 mL. This converter uses US units.
- Fluid ounces vs ounces. Fluid ounces measure volume, ounces measure weight. A US fluid ounce of water weighs about 1.04 oz; for flour or sugar the numbers diverge a lot.
- Cups are volume. A cup of flour weighs about 120–130 g; a cup of sugar about 200 g. Recipes that give grams are more reliable than cup measures.
- Tons. A US short ton is 2,000 lb (907 kg); a UK long ton is 2,240 lb (1,016 kg); a metric tonne is 1,000 kg (2,205 lb).
- Miles per hour vs knots. Aviation and shipping use knots (nautical miles per hour); a nautical mile is 1,852 m, based on one minute of latitude.
Sensible precision
Convert to the precision the situation needs, not the precision the calculator shows. A 5 km run is 3.1 miles, not 3.10686 miles; a 2-inch pipe is 51 mm, not 50.8. When a converted value will be measured or cut, round to what your tape or scale can actually resolve. When it will be used in further calculation, keep the full value and round only at the end.
Common everyday conversions
| Everyday value | Converted |
|---|---|
| Height 5 ft 10 in | 177.8 cm |
| Weight 150 lb | 68.0 kg |
| Speed limit 65 mph | 105 km/h |
| Marathon 42.195 km | 26.22 miles |
| Baby 3.5 kg | 7 lb 11 oz |
| Oven 180 °C | 356 °F (use 350) |
| Fuel 40 mpg (US) | 5.9 L/100 km |
| Paper A4 210 × 297 mm | 8.27 × 11.69 in |
| 1 cup water | 237 mL (≈ 240) |
| Body temperature 37 °C | 98.6 °F |