Everyday Life
Free Unit Converter
Convert between metric and imperial units across eight categories, instantly.
Free to useNo sign-up requiredNo watermarkRuns in your browser
This free unit converter handles eight categories: length, weight, temperature, volume, area, speed, data and time. Pick a category, choose what you are converting from and to, type a number, and the result appears as you type.
Conversions are done through a base unit for each category rather than with a table of hard-coded pairs, so any unit converts to any other unit in the same category without accumulating rounding errors.
How this tool works
Choose a category
Length, weight, temperature, volume, area, speed, data or time. Each category has its own set of units.
Pick your from and to units
Both dropdowns list every unit in the chosen category, so metres to miles and millimetres to inches are equally direct.
Type a value
The converted figure updates as you type. Swap the two units to reverse the conversion without retyping.
How it works
Each category has a base unit - metres for length, kilograms for weight, and so on. Every other unit is defined by its ratio to that base, so a conversion is two steps: into the base, then out to the target unit.
That design means adding a unit does not require defining its relationship with every existing unit, and it keeps results consistent no matter which direction you convert in.
Temperature is the exception, because Celsius, Fahrenheit and Kelvin have different zero points as well as different scales. Those conversions use explicit formulas rather than simple multiplication.
Results are formatted to drop meaningless trailing zeros, so a clean conversion looks clean rather than padded out to six decimal places.
What each category covers
- Length: millimetres, centimetres, metres, kilometres, inches, feet, yards, miles and nautical miles.
- Weight: milligrams, grams, kilograms, tonnes, ounces and pounds.
- Temperature: Celsius, Fahrenheit and Kelvin.
- Volume, area, speed, data and time each have their own metric and imperial units.
Common conversions worth knowing
| 1 inch | 2.54 cm |
|---|---|
| 1 foot | 30.48 cm |
| 1 mile | 1.609 km |
| 1 kilogram | 2.205 pounds |
| 1 pound | 453.6 grams |
| 1 litre | 1.76 UK pints |
| 0 °C | 32 °F |
| 100 °C | 212 °F |
Why temperature is different
Length and weight conversions are pure multiplication, because zero means the same thing in both units - zero metres is zero feet.
Temperature scales do not share a zero. Zero Celsius is the freezing point of water; zero Fahrenheit is something else entirely; zero Kelvin is absolute zero. So converting requires shifting the scale as well as stretching it, which is why 0 °C is 32 °F rather than 0 °F.
Formula
Standard conversion
result = value × (from factor ÷ to factor)
Celsius to Fahrenheit
°F = (°C × 9 ÷ 5) + 32
Fahrenheit to Celsius
°C = (°F − 32) × 5 ÷ 9
Celsius to Kelvin
K = °C + 273.15
Worked examples
10 kilometres to miles
About 6.21 miles - the conversion behind every 10K race.
180 centimetres to feet and inches
180 cm is roughly 5 feet 11 inches, or 70.87 inches.
180 °C to Fahrenheit
356 °F, which is the setting most recipes mean by a moderate oven.
1 gigabyte to megabytes
1,000 MB using decimal gigabytes, which is how storage is usually sold.
Frequently asked questions
Is this unit converter free?
Yes, free with no sign-up. It runs entirely in your browser and keeps working without a connection once the page has loaded.
Which unit categories are supported?
Eight: length, weight, temperature, volume, area, speed, data and time. Each has its own metric and imperial units.
How do I convert Celsius to Fahrenheit?
Multiply by 9, divide by 5, then add 32. So 20 °C is 68 °F. Choose the temperature category above and it does it for you.
Why does temperature need a different formula?
Because the scales have different zero points as well as different sizes of degree, so the conversion has to shift the scale, not just multiply it.
Can I convert between any two units in a category?
Yes. Conversions go through a base unit, so every unit in a category converts directly to every other one.
Guides for this tool
Convert centimeters to inches
One inch is exactly 2.54cm, by international definition - not a rounded approximation. Convert any centimeter measurement to inches instantly and precisely.
Convert kilograms to pounds
A pound is exactly 0.45359237kg, by international definition. Convert any weight between kilograms and pounds instantly and precisely.