Unit conversion is a constant daily need — whether you're following a recipe in a different measurement system, planning a trip between metric and imperial countries, working in engineering, or just trying to understand what a measurement means in familiar terms.
Common Unit Conversions
Length
| Convert | To | Formula |
|---|---|---|
| 1 inch | centimetres | 2.54 cm |
| 1 foot | metres | 0.3048 m |
| 1 mile | kilometres | 1.60934 km |
| 1 kilometre | miles | 0.621371 miles |
| 1 metre | feet | 3.28084 ft |
Weight / Mass
| Convert | To | Formula |
|---|---|---|
| 1 pound (lb) | kilograms | 0.453592 kg |
| 1 kilogram | pounds | 2.20462 lb |
| 1 ounce (oz) | grams | 28.3495 g |
| 1 stone | kilograms | 6.35029 kg |
| 1 tonne | kilograms | 1000 kg |
Temperature
| Convert | Formula |
|---|---|
| Celsius to Fahrenheit | (°C × 9/5) + 32 |
| Fahrenheit to Celsius | (°F − 32) × 5/9 |
| Celsius to Kelvin | °C + 273.15 |
Key reference points: - Water freezes: 0°C = 32°F - Body temperature: 37°C = 98.6°F - Water boils: 100°C = 212°F
Volume
| Convert | To |
|---|---|
| 1 litre | 0.264172 US gallons |
| 1 US gallon | 3.78541 litres |
| 1 US cup | 236.588 mL |
| 1 fluid ounce | 29.5735 mL |
| 1 tablespoon | 14.7868 mL |
| 1 teaspoon | 4.92892 mL |
Speed
| Convert | To |
|---|---|
| 1 mph | 1.60934 km/h |
| 1 km/h | 0.621371 mph |
| 1 m/s | 3.6 km/h |
| 1 knot | 1.852 km/h |
How to Convert Units for Free
iConvertU's Unit Converter handles length, weight, temperature, volume, speed, area, and more.
Step by step
- Open iConvertU Unit Converter
- Select the unit category (length, weight, temperature, etc.)
- Enter your value
- Select the input and output units
- See the converted value instantly
No account required. Conversion is real-time.
Metric vs Imperial: A Quick Reference
Most countries use the metric system. The United States, Liberia, and Myanmar officially use imperial. The UK uses a mix — metric for most things, imperial for road distances (miles) and some informal measurements.
For travellers: - Speed limit signs in the US: miles per hour (mph) — multiply by 1.6 for km/h - Temperature in the US: Fahrenheit — subtract 32, then multiply by 5/9 for Celsius - Distances on US road signs: miles — multiply by 1.6 for kilometres - Petrol prices in the US: per US gallon (3.79 litres)
Area Conversion
| Unit | Equivalent |
|---|---|
| 1 acre | 4,047 m² / 0.4047 hectare |
| 1 hectare | 10,000 m² / 2.471 acres |
| 1 square mile | 640 acres / 2.59 km² |
| 1 square foot | 0.0929 m² |
| 1 square metre | 10.764 sq ft |
Cooking Conversions
Recipes from different countries use different units. Key cooking conversions:
| US Measurement | Metric |
|---|---|
| 1 cup flour | ~125 g |
| 1 cup sugar | ~200 g |
| 1 cup butter | 227 g / 2 sticks |
| 1 cup water/milk | 240 mL |
| 350°F oven | 175°C |
| 400°F oven | 200°C |
| 450°F oven | 230°C |
Note: volume-to-weight conversions for dry ingredients vary by density — cup measurements for flour depend on how tightly it's packed.
Frequently Asked Questions
What is the difference between mass and weight? Mass is the amount of matter in an object (measured in kg, lb). Weight is the gravitational force on that mass (measured in newtons). In everyday life, "weight" and "mass" are used interchangeably because gravitational acceleration is essentially constant on Earth's surface.
Why does the US still use imperial units? The US adopted its own version of the British imperial system before the metric system became standard. Several attempts to adopt metric have failed due to cost of transition and public resistance. The US actually uses SI units in science, medicine, and the military.
Is a UK gallon the same as a US gallon? No. A US gallon is 3.785 litres; a UK (imperial) gallon is 4.546 litres — about 20% larger. UK and US pints also differ: UK pint = 568 mL, US pint = 473 mL.
Is the tool free? Yes. iConvertU Unit Converter is completely free. No account, real-time conversion.
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