Unit converter
Length, mass, volume, temperature, area, speed and data — with every unit shown side by side.
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How this works
One method, every unit
Each category here has a single base unit — the metre for length, the kilogram for mass, the litre for volume. Every other unit is stored as a multiplier against that base, so converting between any two units is two operations: divide into the base, multiply out of it.
result = value × factor(from) / factor(to)
This matters more than it sounds. A conversion table for nine length units would need 72 entries, every one a chance to introduce an error. Storing nine factors instead means all 72 conversions are derived from the same nine numbers and are guaranteed to be mutually consistent.
Temperature is the exception
Temperature scales do not share a zero, so a factor alone is not enough. Each unit also carries an offset:
°C = (°F − 32) × 5/9°C = K − 273.15
There is a consequence worth remembering: you cannot convert a temperature difference with these formulas. A rise of 10 °C is a rise of 18 °F, not 50 °F. The offset applies to a point on the scale, not to an interval along it.
The two scales cross at −40, where Celsius and Fahrenheit read the same number. It is a genuinely useful check: if a converter does not return −40 for −40, something is wrong with it.
Units that share a name but not a size
Several units come in more than one flavour, and mixing them up produces errors large enough to matter.
| Unit | The ambiguity |
|---|---|
| Gallon | Imperial is about 20% larger than US |
| Fluid ounce | US ≈ 29.57 ml, imperial ≈ 28.41 ml |
| Cup | US ≈ 237 ml, metric 250 ml, Japanese 200 ml |
| Ton | Metric 1,000 kg, US short ton ≈ 907 kg, UK long ton ≈ 1,016 kg |
Where a unit is ambiguous, this converter names the variant explicitly rather than picking one silently. Cooking is where this bites most often: an American recipe calling for a cup of liquid means about 237 ml, not the 250 ml a metric measuring jug will give you.
Decimal and binary data sizes
Data size is the one category where two competing systems are both in daily use. The decimal prefixes (KB, MB, GB) step by 1,000. The binary prefixes (KiB, MiB, GiB) step by 1,024, matching how memory is actually addressed.
The gap widens at every step: 2.4% at kilobytes, 4.9% at megabytes, 7.4% at gigabytes, and 10% at terabytes. Both are listed here so you can see the discrepancy directly rather than wondering where the missing space went.
Reading the full list
Below the result, the same value appears in every unit of the current category at once. This is usually faster than converting one pair at a time, particularly when you are checking whether a figure is plausible: seeing 180 cm alongside 5.9 ft and 70.9 in tells you immediately whether you typed the right number.
Common questions
- Why is a US gallon different from a UK gallon?
- They descend from different historical standards. The US gallon was fixed to the old English wine gallon of 231 cubic inches; the imperial gallon was redefined in 1824 as the volume of ten pounds of water. The imperial gallon is about 20% larger. Both are listed separately here, because quietly picking one is how recipes and fuel figures go wrong.
- What is the difference between GB and GiB?
- A gigabyte is 1,000³ bytes; a gibibyte is 1,024³. Storage manufacturers use the decimal definition, while most operating systems report the binary one. That is the entire explanation for why a "1 TB" drive shows up as about 931 GB: it really does hold a trillion bytes, but the computer is dividing by 1,024 three times instead of 1,000.
- Why does temperature need a different kind of conversion?
- Because the scales do not share a zero point. Length, mass and volume conversions are pure multiplication — half of two metres is one metre in every unit. Temperature needs an offset as well as a factor, which is why 0 °C is 32 °F rather than 0 °F, and why you cannot convert a temperature difference the same way you convert a temperature.
- How exact are these figures?
- The factors are the exact defined values, not rounded approximations. An inch is exactly 25.4 mm and a pound is exactly 0.45359237 kg, by international agreement since 1959. The calculation carries full precision internally; only the display is rounded.
- What is a tsubo?
- A Japanese unit of area still used in property listings, equal to two tatami mats. It is defined as exactly 400/121 square metres, about 3.31 m². Floor areas in Japan are frequently quoted in both tsubo and square metres, which makes converting between them a common daily task.