Convert between metric and imperial instantly — cm↔inches, kg↔lbs, °C↔°F, litres↔gallons. Results update as you type.
Whether you are following a recipe written in another country, checking your height for a form, weighing luggage before a flight or reading a thermostat abroad, you eventually need to convert between two systems of measurement. This unit converter handles the four conversions people search for most — length, weight, temperature and volume — and it does the maths the instant you type, with no "Calculate" button, no pop-ups and no sign-up. Pick a category, choose your two units, type a number, and the answer appears in real time. You can even tap the swap arrow to reverse the direction.
The world runs on two parallel measurement systems. Most countries use the metric system (metres, grams, litres, degrees Celsius), built around powers of ten, while the United States and, for many everyday purposes, the United Kingdom still lean on imperial units (inches, feet, miles, pounds, gallons, degrees Fahrenheit). Converting between them is not hard, but the factors are easy to forget — and getting them wrong on a recipe, a medical dose or a building measurement has real consequences. A reliable converter removes that risk.
Every conversion in this tool is built on a small set of exact ratios. Length, weight and volume are simple multiplications — you multiply by a fixed factor. Temperature is the exception: because the Celsius and Fahrenheit scales start at different zero points, you have to add or subtract as well as multiply. Here are the most common factors so you can sanity-check any result.
| Conversion | Multiply by | Quick check |
|---|---|---|
| Inches → centimetres | 2.54 | 1 in = 2.54 cm |
| Centimetres → inches | 0.3937 | 1 cm ≈ 0.39 in |
| Feet → metres | 0.3048 | 1 ft = 0.3048 m |
| Miles → kilometres | 1.60934 | 1 mi ≈ 1.61 km |
| Kilograms → pounds | 2.20462 | 1 kg ≈ 2.2 lb |
| Pounds → kilograms | 0.453592 | 1 lb ≈ 0.45 kg |
| Ounces → grams | 28.3495 | 1 oz ≈ 28.35 g |
| Litres → US gallons | 0.264172 | 1 L ≈ 0.26 gal |
| US gallons → litres | 3.78541 | 1 gal ≈ 3.79 L |
| Celsius → Fahrenheit | ×9/5 + 32 | 20 °C = 68 °F |
For length, weight and volume, zero means zero in both systems — zero metres is zero feet — so a single multiplication does the job. Temperature scales do not share a zero. Water freezes at 0 °C but at 32 °F, so converting Celsius to Fahrenheit requires two steps: multiply by 9/5 (1.8) and then add 32. To go the other way, subtract 32 first, then multiply by 5/9. This is why 0 °C equals 32 °F, 37 °C (body temperature) equals 98.6 °F, and 100 °C (boiling) equals 212 °F. The converter above applies the correct formula automatically for whichever direction you pick.
| You have | It equals | Where you'll need it |
|---|---|---|
| 180 cm | 5 ft 11 in | Height on a US form |
| 70 kg | 154 lb (11 st) | Weight / luggage limits |
| 500 g flour | 17.6 oz | Following an EU recipe in the US |
| 1 US cup | 237 ml | US recipe in a metric kitchen |
| 60 mph | 97 km/h | Driving abroad |
| 180 °C oven | 356 °F (gas mark 4) | Baking from a UK recipe |
Values are rounded for everyday use. Use the live converter above for precise figures.
Watch out for two kinds of gallon. A US gallon is 3.785 litres, but an imperial (UK) gallon is 4.546 litres — about 20% larger. This converter uses the US gallon, the most-searched version online; if you are in the UK, remember your gallon holds more. The same applies to pints and fluid ounces, which differ between the two systems.
Round only at the end. When a conversion is one step in a longer calculation — say, scaling a recipe and then converting — keep the full decimals until your final number. Rounding 0.3937 to 0.4 looks harmless but compounds into a noticeable error over large quantities. Sanity-check against a known anchor: 1 inch is about the width of a thumb, 1 kg is roughly 2.2 lb, and room temperature is around 20 °C / 68 °F. If a result is wildly off those anchors, you probably picked the wrong direction — tap the swap arrow and try again.
Divide the centimetre value by 2.54, or multiply by 0.3937. For example, 180 cm ÷ 2.54 ≈ 70.9 inches, which is 5 feet 11 inches. The converter above does this instantly when you choose Length, centimetres → inches.
Multiply the kilogram value by 2.20462. So 70 kg × 2.20462 ≈ 154.3 pounds. To go from pounds back to kilograms, multiply by 0.453592 instead.
Multiply the Celsius value by 9/5 (1.8) and add 32: °F = °C × 1.8 + 32. For example, 20 °C × 1.8 + 32 = 68 °F. To convert Fahrenheit to Celsius, subtract 32 first, then multiply by 5/9.
No. A US gallon is about 3.785 litres, while an imperial (UK) gallon is about 4.546 litres — roughly 20% larger. This converter uses the US gallon. Keep that difference in mind for fuel economy and recipes.
Small differences come from rounding the conversion factors or from US versus imperial definitions of pints, ounces and gallons. This tool keeps full precision internally and rounds only the displayed result, so it stays accurate for everyday use.