Unit Converter
Pick a family of units, enter a value and the unit it is in, and this converts it into every other unit in that family at once.
Converted
1.0000m
- mm
- 1,000.0000
- cm
- 100.0000
- m
- 1.0000
- in
- 39.3701
- ft
- 3.2808
- yd
- 1.0936
- Conversions use exact factors — an inch is exactly 25.4 millimetres by definition, not 25 and a bit — so these will not drift from the rounded numbers people memorise.
About the unit converter
Most conversions people do from memory use rounded factors — an inch is about two and a half centimetres, a kilogram is roughly two point two pounds. That is fine for a rough answer and gradually wrong for anything that compounds, which is where a converter earns its keep.
The factors here are the defined ones. An inch is exactly 25.4 millimetres, by international agreement since 1959; a pound is exactly 0.45359237 kilograms. These are definitions rather than measurements, so they do not drift and there is no rounding error to accumulate.
Showing every unit in the family at once is deliberate. Half the time the question is not really "what is this in metres" but "which of these units makes this number readable", and having them side by side answers that immediately.
What it works out
- Length — mm, cm, m, inches, feet, yards
- Weight — grams, kilograms, pounds, tons and tonnes
- Area — square feet, metres, yards, acres, hectares
- Volume — litres, cubic feet and metres, US and imperial gallons
The formula
result = value × (metres per from-unit) ÷ (metres per to-unit)
Every conversion goes through a base unit rather than being defined pair by pair. Length converts through metres, weight through kilograms, area through square metres, volume through cubic metres. That means one table of factors handles every combination instead of needing a factor for each pair.
It also means the same code that converts a room measurement also converts a concrete order, which is how the rest of this site works — every calculator does its arithmetic in base units and converts only at the edges.
The factors are exact where the definitions are exact. An inch is 25.4 millimetres precisely, a pound is 0.45359237 kilograms precisely, and a US gallon is 3.785411784 litres precisely. None of these are approximations; they are the legal definitions.
Two traps are worth naming. Squared units square their factor — a square yard is nine square feet, not three — and cubed units cube it, so a cubic yard is twenty-seven cubic feet. And gallons are not universal: a US gallon is about 3.79 litres while an imperial gallon is about 4.55, a difference of a fifth.
- Value
- The number you are converting.
- From
- The unit it is currently in.
- To
- Every other unit in the same family, all shown at once.
A worked example
One metre, converted into every other length unit.
That works out to 1.0000 m.
- mm
- 1,000.0000
- cm
- 100.0000
- m
- 1.0000
- in
- 39.3701
- ft
- 3.2808
- yd
- 1.0936
Questions
How many centimetres in an inch?
Exactly 2.54, by definition rather than by measurement. That makes an inch exactly 25.4 millimetres and a foot exactly 30.48 centimetres.
How many pounds in a kilogram?
About 2.20462. The exact definition runs the other way: a pound is precisely 0.45359237 kilograms.
How many square feet in a square yard?
Nine. Squaring a length squares its conversion factor, so a three-foot yard becomes a nine-square-foot square yard. The same effect makes a cubic yard twenty-seven cubic feet.
Is a US gallon the same as an imperial gallon?
No, and the gap is large. A US gallon is about 3.785 litres and an imperial gallon about 4.546 — roughly twenty per cent bigger. Both are listed separately here for that reason.
What is the difference between a ton and a tonne?
A tonne is 1,000 kilograms, about 2,205 pounds. A US short ton is 2,000 pounds, about 907 kilograms. A UK long ton is 2,240 pounds. All three are in the weight list.
Why not just use rounded factors?
They are fine for a mental estimate and gradually wrong for anything that multiplies up. Using 2.5 rather than 2.54 for an inch is a 1.6% error, which is invisible on one measurement and expensive across a large order.