How to Convert Units Online — The Complete Guide
Unit conversion trips up almost everyone eventually. Cooking a recipe that uses cups when you only have a kitchen scale. Buying fabric in yards when you think in metres. Checking if a temperature in Celsius is actually cold before packing for a trip. An online unit converter handles all of these instantly — no formula memorisation required.
The unit categories you'll actually use
Length and distance: The most common everyday conversion. Centimetres to inches, metres to feet, kilometres to miles — particularly useful for international travel, clothing sizing, and recipe measurements. The quick reference: 1 inch = 2.54cm, 1 foot = 30.48cm, 1 mile = 1.609km.
Weight and mass: Kilograms to pounds, grams to ounces. Essential for cooking (especially US recipes in metric countries and vice versa), gym progress tracking, and shipping calculations. Quick reference: 1kg = 2.205 lbs, 1 oz = 28.35g.
Temperature: Celsius and Fahrenheit don't convert with a simple multiplication — the formula is °F = (°C × 9/5) + 32. A few anchor points worth knowing: 0°C = 32°F (freezing), 20°C = 68°F (comfortable room temperature), 37°C = 98.6°F (body temperature), 100°C = 212°F (boiling).
Volume: Litres to gallons, millilitres to fluid ounces, cups to millilitres. Cooking conversions between US customary and metric are especially useful for international recipes. 1 US cup = 236.6ml, 1 US gallon = 3.785 litres.
Speed: Kilometres per hour to miles per hour — primarily useful when driving abroad. 100 km/h = 62.1 mph. Speed limit signs in the UK are in mph; most of Europe uses km/h.
International cooking conversions
US recipes predominantly use cups, tablespoons, and teaspoons. UK and Australian recipes use grams and millilitres. The difference matters most when baking, where precision affects texture and rise. Converting by weight (grams) rather than volume (cups) is actually more accurate for dry ingredients, since a cup of flour can vary in weight by 20–30% depending on how it's scooped.
Most useful baking conversions: 1 cup flour ≈ 120–130g, 1 cup sugar ≈ 200g, 1 cup butter = 227g = 2 sticks US. A kitchen scale removes the ambiguity entirely, but a unit converter gets you close enough for most recipes.
Using the unit converter
Enter the value you have, select the unit it's in, and choose the unit you want to convert to. The result appears immediately. For temperature, length, weight, volume, speed, area, and more — all in a single tool, no switching between different converters for different categories.
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Open Unit Converter →Frequently Asked Questions
How do I convert kilometres to miles?
Multiply kilometres by 0.6214. Or use the shorthand: 1 km ≈ 0.621 miles. Quick anchor: 100 km/h is approximately 62 mph. For precise conversions, use our free unit converter.
How do I convert Celsius to Fahrenheit?
The formula is °F = (°C × 9/5) + 32. For a quick estimate, double the Celsius value and add 30. Key anchors: 0°C = 32°F (freezing), 20°C = 68°F (comfortable room temp), 100°C = 212°F (boiling).
How many cups is 250ml?
250ml is approximately 1.06 US cups — close enough to 1 cup for most cooking purposes. For baking where precision matters, 250ml = 1 metric cup (Australian/Canadian standard), which differs slightly from the US cup (236.6ml).
How do I convert kg to pounds?
Multiply kilograms by 2.205. So 70kg = 154.3 lbs. For a quick estimate: multiply by 2 and add 10%. Quick reference: 1kg = 2.205 lbs, 1 lb = 0.454 kg.
Can I convert area and volume units online?
Yes. Our free unit converter handles length, weight, temperature, volume, speed, area, and more in a single tool. No separate converters needed for different unit types.