How to convert units
- Type the value you want to convert.
- Pick the unit you are converting from.
- Pick the unit you want.
- Press Convert or watch the live result.
- Read the other units listed below the answer.
What this unit converter gives you
- Distance in meters and kilometers plus feet and miles.
- Volume in liters, milliliters and both kinds of gallon.
- UK pints which differ from US pints by about a fifth.
- The conversion factor shown both ways.
- Every other unit listed so you rarely convert twice.
- Live results with nothing sent anywhere.
The two gallons problem
A US gallon holds 3.785 liters. A UK gallon holds 4.546 liters. That is a gap of about 20 percent. Both still go by the name gallon.
The gap shows up all the time. American fuel economy in miles per gallon does not match British figures. A car that gets 30 mpg in the US gets about 36 mpg by the UK measure. Recipes in American cups and pints do not scale to British measures. Paint coverage, tank sizes and cleaning mixes carry the same risk.
The pint follows the gallon. A UK pint holds 568 milliliters. A US pint holds 473. A pint of beer in London really is bigger than one in New York. It is not a rounding gap.
Why the two systems split apart
Both systems grew from old English units. The United States kept the old wine gallon of 231 cubic inches after independence. Britain redefined its gallon in 1824 as the volume of ten pounds of water. The two never came back together. Every unit built on the gallon carries the difference.
Length units did come back together. An international agreement in 1959 fixed the inch at exactly 25.4 millimeters for both countries. So distance conversions are exact. Volume conversions depend on which country you mean.
Units that only look the same
| Unit | How it differs |
|---|---|
| Fluid ounce | US and UK versions differ by about 4 percent |
| Cup | 240 ml in the US and 250 ml in Australia |
| Ton | Metric, US short and UK long tons all differ |
| Mile | Statute and nautical miles differ by about 15 percent |
Here is a safe habit for any recipe or spec from another country. Check which system the units belong to before you convert. Do not wait until the result looks wrong.
A unit converter does not scale
A conversion changes the unit and keeps the amount the same. Two liters and 2000 milliliters hold the same liquid. A scale step changes the amount and keeps the proportions. A double batch of a recipe is one example.
A mix up between the two gives some odd results. Does a recipe need both? Convert first and scale second. The ratio calculator handles the scaling part. That order keeps rounding errors small.
A quick unit converter example
A British recipe calls for 2 UK pints of stock. Enter 2 and pick UK pints. Choose milliliters as the target. The tool shows about 1137 ml. The list below also shows about 2.4 US pints. Now you can measure it with an American jug.
Why the US still uses customary units
The United States is one of very few countries that use customary units in daily life. Science, medicine and the military in the US mostly use metric. Food labels show both. Road signs and recipes stay customary. So Americans who travel or work with global teams switch systems often. A quick tool saves guesswork and costly mistakes.
NASA lost the Mars Climate Orbiter in 1999 after a unit mix up between teams. One side used pound force and the other used newtons. Small mistakes at home cost less. They still waste time and money.
Tips for accurate conversions
- Note the country of any recipe or manual.
- Use metric when you share specs across borders.
- Round only at the last step.
- Measure liquids by weight when a recipe allows it.
Who uses a unit converter?
Cooks follow foreign recipes. Travelers read road signs and fuel prices. Students solve science homework. DIY fans buy paint and fuel. Online shoppers compare product sizes.
Your numbers stay private
The tool runs in your browser and sends nothing. Need more length units? Use the length converter. Want pounds and kilograms? Try the weight converter. Want the weather abroad in Fahrenheit? The temperature converter helps.