Unit Converter
Six categories, all the everyday units, converted as you type.
Conversions people look up most
| From | To | Multiply by |
|---|---|---|
| Miles | Kilometres | 1.609 |
| Feet | Metres | 0.3048 |
| Pounds | Kilograms | 0.4536 |
| US gallons | Litres | 3.785 |
| Inches | Centimetres | 2.54 |
Temperature is the odd one out — it needs an offset, not just a factor: °F = °C × 9/5 + 32. Quick mental version: double the Celsius and add 30 (accurate within a couple of degrees for everyday weather).
Watch out for the two gallons (and pints, and fluid ounces)
A US gallon is 3.785 L; a UK (imperial) gallon is 4.546 L — 20% bigger. The same split affects pints and fluid ounces, which is why a "pint" in a London pub is larger than one in New York. This converter includes both variants; recipe conversions especially deserve the right one.
Mental shortcuts worth memorising
You won't always have a converter open. These approximations are close enough for shopping, cooking and travel:
| Conversion | Quick method | Accuracy |
|---|---|---|
| km → miles | Multiply by 0.6 | Within 4% |
| miles → km | Add half again, then a bit | Within 3% |
| °C → °F | Double it and add 30 | ±3° in everyday range |
| kg → lb | Double it, add 10% | Within 1% |
| cm → inches | Divide by 2.5 | Within 2% |
| litres → US gallons | Divide by 4 | Within 6% |
The temperature one is the most useful abroad: 20°C → about 70°F, 30°C → about 90°F. Both are within a couple of degrees, which is all you need to decide what to wear.
Reference points that make units intuitive
- A metre is roughly one long stride, or from your nose to your outstretched fingertips.
- A kilogram is a litre of water, or a large bag of sugar.
- An inch is about the top joint of your thumb.
- A hectare is roughly two football pitches; an acre is a bit under half of that.
- 100 km/h is about 62 mph — the difference that catches out drivers crossing between Canada and the US.
Where conversion errors do real damage
Recipes are the everyday case: a US cup is 237 mL while a metric cup is 250 mL, and baking is unforgiving about it — which is why serious bakers weigh in grams instead. Medication dosing is the serious case, where confusing millilitres with teaspoons has caused documented harm; always use the marked syringe or cup rather than kitchen spoons. And in engineering, unit mismatches have destroyed spacecraft — NASA's Mars Climate Orbiter was lost in 1999 because one team worked in pound-force seconds while another used newton-seconds.