Unit converter · Free · No sign-up
Unit Converter
A unit converter changes a measurement from one unit to another, such as miles to kilometres or cups to millilitres. This one covers length, weight, volume, area, speed and temperature in 48 metric, US and UK units, uses the exact defined factors, and shows the amount in every unit of its kind at once.
Shown to 10 significant figures. Nothing leaves this browser.
| millimetres | 1,609,344 |
|---|---|
| centimetres | 160,934.4 |
| metres | 1,609.344 |
| kilometres | 1.609344 |
| inches | 63,360 |
| feet | 5,280 |
| yards | 1,760 |
| nautical miles | 0.8689762419 |
Pick what you are measuring, type the amount and choose the two units. The answer updates as you type, the line under it gives the rate for one unit, and the table shows the same amount in every other unit, so the next question is already answered.
Unit conversion multiplies a measurement by a fixed factor between two units of the same quantity: an inch is exactly 25.4 mm, so 12 inches is 304.8 mm. Temperature is the exception, because its scales start from different zeros and need a formula.
- No sign-up
- Nothing sent anywhere
- Exact factors
- Metric, US and UK units
Key facts
| Detail | Answer |
|---|---|
| Price | Free, no sign-up, nothing to install |
| Measures | Length, weight, volume, area, speed and temperature |
| Units | 48 in all: 9 length, 7 weight, 14 volume, 10 area, 5 speed, 3 temperature |
| Factors | Exact defined values: 1 in = 25.4 mm, 1 lb = 0.45359237 kg, 1 US gal = 3.785411784 L, 1 UK gal = 4.54609 L |
| Temperature | By formula: °F = °C × 9/5 + 32, K = °C + 273.15 |
| US and UK measures | Both, each labelled: pints, gallons and fluid ounces, and US and metric cups |
| Display | Rounded once, to 10 significant figures; very large or small values in e notation |
| Every unit at once | The table under the result shows the amount in every unit of the same kind |
| Where amounts go | Nowhere: converted in your browser |
How to convert units
Three choices and the answer, which updates as you type.
Pick what you are measuring
Length, weight, volume, area, speed or temperature. Each opens on the pair people convert most, such as miles to kilometres.
Type the amount
Decimals with a point; a comma between thousands is fine, so 1,500 reads as 1500.
Choose the two units
From and To. US and UK measures with the same name are listed separately.
Swap if it is backwards
The arrows between the two units turn the conversion round.
Read the answer and the rate
The line under the answer gives one unit’s worth, or the formula for temperature.
Check the table for the rest
The same amount in every other unit of that kind, so 1 mile is also there in feet, yards and nautical miles.
What people convert, and why
Most conversions happen where a metric country meets an imperial recipe, road or scale.
Cooking and baking
US cups and tablespoons into millilitres, and oven temperatures between °F and °C.
Travel and driving
Miles and kilometres, and speed limits between mph and km/h: 100 km/h is 62.14 mph.
Running and fitness
Race distances, 5 km is 3.11 miles, and body weight in kilograms, pounds or stone.
DIY and building
Feet and inches into millimetres, and floor areas between square feet and square metres.
Land and property
Acres and hectares: one hectare is 2.47 acres.
Sailing and flying
Knots and nautical miles, which are defined from the metre: a nautical mile is exactly 1,852 m.
Common conversions at a glance
The conversions people look up most, worked out by the converter above and shown to its ten significant figures. Round them to suit: two decimal places is plenty for a recipe or a road sign.
| From | Equals |
|---|---|
| 1 inch | 2.54 cm |
| 1 foot | 30.48 cm |
| 1 mile | 1.609344 km |
| 1 kilometre | 0.6213711922 miles |
| 1 metre | 3.280839895 feet |
| 5 km (a parkrun) | 3.106855961 miles |
| 1 kilogram | 2.204622622 pounds |
| 1 pound | 453.59237 g |
| 1 ounce | 28.34952313 g |
| 1 stone | 6.35029318 kg |
| 1 US cup | 236.5882365 ml |
| 1 US tablespoon | 14.78676478 ml |
| 1 US pint | 473.176473 ml |
| 1 UK pint | 568.26125 ml |
| 1 US gallon | 3.785411784 litres |
| 1 UK gallon | 4.54609 litres |
| 1 square metre | 10.76391042 sq ft |
| 1 acre | 0.4046856422 hectares |
| 1 hectare | 2.471053815 acres |
| 1 mph | 1.609344 km/h |
| 100 km/h | 62.13711922 mph |
| 1 knot | 1.852 km/h |
Same name, different size: the conversions people get wrong
Several everyday units share a name but not a size, depending on the country. These are the ones that catch people out most often, and the reason the converter labels each one US, UK or metric instead of guessing.
- Pints. A US liquid pint is 473 ml. A UK (imperial) pint is 568 ml, about a fifth larger.
- Fluid ounces. A US fluid ounce is 29.57 ml and a UK fluid ounce 28.41 ml. The UK ounce is the smaller one, yet the UK pint is the larger, because a UK pint holds 20 fluid ounces and a US pint 16.
- Cups. A US customary cup is 236.6 ml, a metric cup is 250 ml, and recipes rarely say which they mean.
- Gallons. A US gallon is 3.785 litres and a UK gallon 4.546 litres, which matters for fuel economy figures quoted in miles per gallon: the same car does more miles to the UK gallon.
- Tons. A tonne is 1,000 kg. A US short ton is 2,000 lb, 907.18474 kg, and a UK long ton 2,240 lb, 1,016.0469088 kg. The converter carries the tonne.
- Stone. One stone is 14 pounds, 6.35029318 kg, and is still the usual way to state body weight in the UK and Ireland.
Cups to grams is not a unit conversion
A cup is a volume and a gram is a weight, so how many grams fit in a cup depends on what is in it: a cup of flour weighs much less than a cup of sugar. A converter that turns cups into grams without asking the ingredient is using one ingredient’s density for all of them. This one keeps volume and weight apart rather than give an answer that is right for water and wrong for flour.
Temperature: why it needs a formula, not a factor
Length, weight and volume all start from zero together: zero inches is zero centimetres. Temperature scales do not. Water freezes at 0 °C but at 32 °F, and kelvin starts at absolute zero, so converting needs a formula with an offset, not just a factor.
- Celsius to Fahrenheit: °F = °C × 9/5 + 32
- Fahrenheit to Celsius: °C = (°F − 32) × 5/9
- Celsius to kelvin: K = °C + 273.15
| °C | °F | K | |
|---|---|---|---|
| Absolute zero | −273.15 | −459.67 | 0 |
| Where the two scales meet | −40 | −40 | 233.15 |
| Water freezes | 0 | 32 | 273.15 |
| A mild room | 20 | 68 | 293.15 |
| Body temperature, as usually quoted | 37 | 98.6 | 310.15 |
| Water boils, at sea level | 100 | 212 | 373.15 |
| A moderate oven | 180 | 356 | 453.15 |
Recipes round oven temperatures: 180 °C is printed as 350 °F, which is really 176.67 °C. For a rough conversion in your head, double the Celsius figure and add 30. It gives 70 for 20 °C against the true 68, close enough for the weather and not for an oven.
Where the exact factors come from
Most conversion factors are not measurements but definitions, fixed by agreement, which is why the converter can be exact.
| Unit | Defined as | Since |
|---|---|---|
| Yard | 0.9144 m exactly | The 1959 international yard and pound agreement |
| Inch, foot, mile | 25.4 mm; 0.3048 m; 1,609.344 m | Follow from the yard |
| Pound | 0.45359237 kg exactly | The same 1959 agreement |
| Ounce, stone | 1/16 lb; 14 lb | Follow from the pound |
| US gallon | 231 cubic inches, 3.785411784 L | Follows from the inch |
| UK gallon | 4.54609 L exactly | The UK Weights and Measures Act 1985 |
| Nautical mile | 1,852 m exactly | International agreement, 1929 |
| Acre | 4,840 square yards, 4,046.8564224 m² | Follows from the yard |
Why rounded factors drift
Using 2.2 pounds to the kilogram is 0.2% out. That is nothing for a suitcase, but repeated through a long calculation, or converted there and back, the error shows. The converter keeps the exact factor all the way through and rounds once, at the end, for display.
One unit that used to have two sizes no longer does: the US survey foot, a hair longer than the international foot, was retired for new work in the US at the start of 2023. The foot here is the international foot, 0.3048 m.
This converter, a search engine, a spreadsheet or an app
All of these will turn miles into kilometres. They differ in how much they show at once and how clearly they say which pint or gallon they mean.
| This converter | Search engine box | Spreadsheet CONVERT() | Converter app | |
|---|---|---|---|---|
| Every unit of the kind at once | Yes, in a table | One pair at a time | One formula a cell | Varies |
| US and UK measures told apart | Yes, labelled | Yes | Yes, by unit code | Varies |
| The factor or formula shown | Yes, under the result | Sometimes | In the documentation | Rarely |
| Install or account | None | None | A spreadsheet app | An install |
| Best for | One amount, every unit | A quick single answer | A column of figures | Offline, on a phone |
Frequently asked questions
How many centimetres are in an inch?
Exactly 2.54. The inch has been defined as 25.4 millimetres since 1959, so 12 inches is 30.48 cm.
How do you convert miles to kilometres?
Multiply by 1.609344. 10 miles is 16.09344 km. Going the other way, multiply kilometres by 0.6213711922, so 5 km is 3.106855961 miles.
How do you convert kilograms to pounds?
Divide by 0.45359237, or multiply by about 2.2046. 70 kg is 154.3235835 lb, or 11.02 stone.
How do you convert Celsius to Fahrenheit?
Multiply by 9/5 and add 32. 20 °C is 68 °F and 100 °C is 212 °F. To go back, subtract 32 and multiply by 5/9.
Is a US pint the same as a UK pint?
No. A US liquid pint is 473.176473 ml and a UK pint 568.26125 ml, about a fifth more. Gallons differ the same way: 3.785 litres in the US, 4.546 in the UK.
How many millilitres are in a cup?
A US cup is 236.5882365 ml and a metric cup 250 ml. Recipes from the US mean the first; recipes from Australia, New Zealand and Canada often mean the second.
How many square feet are in a square metre?
10.76391042. A square foot is exactly 0.09290304 square metres, so 1,000 sq ft is 92.90304 m².
Can I convert cups to grams?
Not as a unit conversion. A cup measures volume and a gram measures weight, so the answer depends on the ingredient’s density. This converter keeps volume and weight separate.
Why are results shown to 10 significant figures?
So that exact conversions show in full, such as 1 mile = 1.609344 km, while long ones are cut where the digits stop meaning anything. Every factor is exact; only the display is rounded.
Does the converter send what I type anywhere?
No. The conversion runs in your browser and the amounts never reach a server.
Related guides
Where units change the answer.