About the Unit Converter
This free unit converter handles length, weight, temperature, area, volume, speed, data and time — metric and imperial together. Pick a category, choose the units, and the result updates as you type.
It runs in your browser — nothing is uploaded, and it works with no connection.
Temperature is the odd one out
Every other conversion here is a multiplication. Temperature is not, and that is why it gets its own explanation.
Metres to feet is a single factor: multiply by 3.28084. The scale starts at zero in both systems, so doubling one doubles the other.
Celsius and Fahrenheit do not share a zero. Water freezes at 0°C and 32°F. So converting needs a shift as well as a scale:
- C to F — multiply by 9/5, then add 32
- F to C — subtract 32, then multiply by 5/9
The consequence catches people out: 20°C is not twice 10°C in any meaningful sense, and a 10-degree rise in Celsius is an 18-degree rise in Fahrenheit. Temperature *differences* convert with the factor alone; temperature *values* need the offset too.
Kelvin is the scientific scale and starts at absolute zero, the coldest anything can be. It shares Celsius's step size, so converting is just K = °C + 273.15. A Kelvin value is never negative.
Two worth memorising: −40 is the same in both Celsius and Fahrenheit, the one point where the scales cross. And 28°C ≈ 82°F, a handy digit-swap coincidence for weather.
US gallons are not UK gallons
The most dangerous unit trap in everyday use, because both are called a gallon.
A US gallon is 3.785 litres. An imperial (UK) gallon is 4.546 litres — about 20% larger. Pints follow the same split: a US pint is 473 ml, a UK pint is 568 ml.
This matters in recipes and in fuel figures. An American recipe calling for a cup means 237 ml; a metric cup is 250 ml; an Australian cup is also 250 ml but their tablespoon is 20 ml against the US 15 ml. In baking, where ratios decide whether something works, these differences are enough to ruin the result.
The volume units in this converter are US measures, labelled as such. If you are following a British recipe, check which system it uses before converting — and for baking, weight is far more reliable than volume anyway.
Ounces of weight, ounces of space
Another word doing two jobs.
An ounce (oz) is a unit of weight — 28.35 grams.
A fluid ounce (fl oz) is a unit of volume — about 29.6 ml in the US, 28.4 ml in the UK.
They are not interchangeable, and they only coincide roughly for water. Eight fluid ounces of honey weighs considerably more than eight ounces; eight fluid ounces of flour weighs considerably less. Whenever a recipe says "ounces", the question is whether it means weight or volume — and for dry ingredients it almost always means weight.
Kilobytes: 1000 or 1024?
Both, depending on who is counting, and this is why your new drive looks smaller than the box said.
Storage manufacturers use powers of 1000. A "1 TB" drive holds 1,000,000,000,000 bytes.
Windows reports using powers of 1024. It divides that same number by 1024 three times and displays 931 GB.
Nothing is missing and nobody is cheating — the two are counting in different bases. The difference grows with size: about 2.4% at kilobytes, 7% at gigabytes, nearly 10% at terabytes.
The standards bodies introduced KiB, MiB, GiB for the 1024-based units, leaving KB, MB, GB for 1000. macOS and Linux mostly follow this; Windows still labels 1024-based values as GB. This converter uses the decimal (1000-based) definitions.
How to use it
- Choose a category (length, weight, temperature…)
- Enter a value and pick the from and to units
- The converted value appears instantly — use Swap to reverse the direction
Good to know
- Area and volume scale by powers. Doubling a length quadruples the area and multiplies volume by eight. A square metre is not 100 square centimetres — it is 10,000.
- A tonne is not a ton. A metric tonne is 1000 kg; a US short ton is 907 kg; a UK long ton is 1016 kg.
- A stone is 14 pounds, used for body weight mainly in Britain and Ireland.
- A nautical mile is 1852 m, longer than a land mile, and a knot is one nautical mile per hour.
- Round sensibly. Converting 10 cm to 3.937007874 inches implies a precision your measurement never had.
- A "year" is an approximation. Here it is 365 days; the real figure is about 365.2425, which is what leap years exist to correct.
Common questions
How do I convert Celsius to Fahrenheit?
Multiply by 9/5 and add 32, so 20°C becomes 68°F. Going back, subtract 32 first and then multiply by 5/9. The addition is what makes temperature different from every other conversion — the two scales do not share a zero point, so a simple multiplication would give the wrong answer.
Why is a US gallon different from a UK gallon?
They are genuinely different units that ended up sharing a name. A US gallon is 3.785 litres and an imperial gallon is 4.546 litres, around 20% larger, and the same split applies to pints and fluid ounces. The US kept older English measures while Britain redefined its own in 1824. Always check which system a recipe or a fuel figure is using.
Is an ounce a weight or a volume?
Both words exist. An ounce is a weight of 28.35 grams; a fluid ounce is a volume of roughly 29.6 ml in the US. They match only approximately for water, so eight fluid ounces of honey weighs far more than eight ounces. Recipes measuring dry ingredients in ounces almost always mean weight.
Why does my 1 TB hard drive show as only 931 GB?
Because the manufacturer counted in powers of 1000 and Windows displays in powers of 1024. One trillion bytes divided by 1024 three times gives 931, so both numbers describe the same drive. Nothing has been lost. The units KiB, MiB and GiB were created for the 1024-based values, though Windows still labels them GB.
How many centimetres are in an inch?
Exactly 2.54, by definition since 1959 — it is not a rounded approximation. That makes a foot exactly 30.48 cm and a mile exactly 1609.344 m. Going the other way, one centimetre is about 0.3937 inches.
Why isn't a square metre equal to 100 square centimetres?
Because area scales with the square of length. A metre is 100 centimetres, so a square metre is 100 × 100 = 10,000 square centimetres. Volume scales with the cube, so a cubic metre is a million cubic centimetres. Forgetting to square or cube the factor is the most common error in area and volume conversions.
Are my numbers sent anywhere?
No. Every conversion is calculated by your browser as you type, so nothing leaves your device and the tool works offline.
Related tools
- Coordinate Converter — convert between GPS coordinate formats
- Number Base Converter — binary, octal, decimal and hexadecimal
- Timezone Converter — the same idea applied to clocks
- Roman Numeral Converter — a different kind of number conversion
