Unit converter

Length, mass, volume, temperature, area, speed, pressure, energy, fuel economy and data — with UK and US measures kept properly separate.

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The conversions that go wrong most often

UK and US volumes are not the same

UnitUK (imperial)US
Pint568 ml473 ml
Gallon4.546 l3.785 l
Fluid ounce28.4 ml29.6 ml

A US gallon is roughly 17% smaller than a UK one, which is why American miles-per-gallon figures look better than they are. Converting a US MPG figure to UK MPG means multiplying by about 1.2 before anything else.

Temperature has an offset

°F = °C × 9/5 + 32. Because of the +32, a temperature and a temperature difference convert differently. A 10 °C rise is an 18 °F rise. Getting this wrong is a classic error in weather reporting and in heating calculations.

Cups are volume, grams are mass

There is no fixed cup-to-gram conversion, because it depends entirely on what is in the cup:

Ingredient1 US cup ≈
Water237 g
Plain flour120–125 g
Granulated sugar200 g
Butter227 g
Rolled oats90 g

For baking, weighing in grams is simply more reliable than any conversion — flour packs differently depending on how it was scooped, with variation of 20% or more between people using the same cup.

Tons, tonnes and short tons

1 metric tonne = 1,000 kg. 1 UK long ton = 1,016 kg. 1 US short ton = 907 kg. Shipping quotes, carbon figures and scrap prices all use the word "ton" without always saying which.

Data: 1,000 or 1,024?

Storage manufacturers use decimal units — 1 GB = 1,000,000,000 bytes. Operating systems traditionally report binary units (GiB) but label them "GB". This is why a 1 TB drive shows as roughly 931 GB in Windows. Nothing is missing; the two are counting differently.

Quick reference

FromToMultiply by
Inchescm2.54 (exact)
Mileskm1.609
Poundskg0.4536
Stonekg6.350
Feetmetres0.3048 (exact)
Acreshectares0.4047
mphkm/h1.609
PSIbar0.0689

The inch and the foot are defined exactly in metric terms — since 1959 an inch is precisely 25.4 mm by international agreement.

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Common questions

Why does my recipe conversion taste wrong?

Usually UK versus US cups and spoons, or a volume-to-mass conversion applied to the wrong ingredient. A UK tablespoon is 15 ml, an Australian one is 20 ml.

What is a "nautical mile"?

1,852 metres — one minute of latitude. It is not the same as a statute mile (1,609 m), which is why boat and aircraft speeds in knots do not match car speedometers.

Are these conversions exact?

Some are exact by definition (inch, foot, pound, calorie). Others are rounded rational approximations. Palarid keeps full precision internally and rounds only for display.

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