Millimetres to Centimetres Converter
10 mm = 1 cm exactly. Type in either box.
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Ten to one
Ten millimetres make a centimetre. It is the smallest step on the metric ladder that most people use, and the conversion is one decimal place.
1 cm = 10 mm exactly
Both markings appear on the same ruler, which is why this conversion is usually done by eye rather than by arithmetic. 45 mm is 4.5 cm — four and a half of the big divisions.
The millimetre
A thousandth of a metre, and the working unit of engineering drawings, carpentry and anything made to fit. Metric technical drawings are dimensioned in millimetres by default, with no unit written at all.
It is close to the smallest length most people can judge by eye, which is part of why it has stayed the practical unit for made things.
The centimetre
A hundredth of a metre, and the unit of rulers, body measurements and packaging. It is not much used in engineering — drawings jump from millimetres to metres — but it is what most people reach for in everyday life.
Roughly, an inch is two and a half centimetres, which makes 2.54 one of the most useful numbers to memorise.
The working, step by step
Every line updates with whatever you type above. The point is the method, which is the same for any pair of units in this family.
The same quantity, two different numbers
One physical amount, read off two scales. The tick marks do not line up, and the gap between them is the conversion factor made visible.
How much is that?
A number is easier to judge next to something familiar.
Your turn
Reading a method and being able to use it are different things. Answer within half a per cent and it counts as correct.
Score: 0 of 0
How to use this converter
- Type into either box. The other side updates as you go; there is no button to press.
- Swap the direction with the button between the boxes, carrying your value across.
- Set the decimals if the default is more or less precision than you need.
- Copy the answer with its unit, ready to paste.
- Use the shortcut buttons for the values that come up most often.
- Share the result. The address bar tracks what you type, so the link you copy opens on the same number.
Common uses and tips
Where length conversions come up
- Height. Quoted in feet and inches in Britain and America, and in centimetres nearly everywhere else. 5 ft 10 in is 178 cm.
- Buying things online from another market, where the dimensions are in units your tape measure does not have.
- DIY and building, where materials come in metric sizes and older plans are in imperial.
- Screens, tyres and pipes, which stay in inches worldwide even in fully metric countries.
- Running and cycling, where race distances are metric and training apps may report either.
Numbers worth carrying
- 1 inch = 2.54 cm exactly. Everything imperial in this family descends from it.
- 1 foot = 30.48 cm, twelve inches.
- 1 yard = 0.9144 m, a little shorter than a metre.
- 1 mile = 1.609 km, and 1 km = 0.621 mile.
- A metre is about 39.37 inches, or 3 ft 3 in.
Mental shortcuts
Kilometres to miles: multiply by six and drop the last digit. 80 km × 6 = 480, drop the digit for 48 miles, against a true 49.7.
Miles to kilometres: add sixty per cent. 50 miles plus 60 % is 80 km, against a true 80.5.
Centimetres to inches: divide by 2.5 and take off a little. Dividing by 2.5 gives an answer about 1.6 % high.
Mistakes worth avoiding
- Feet and inches are not decimal. 5.5 feet is 5 ft 6 in, not 5 ft 5 in. Multiply the decimal part by twelve.
- Do not use length factors for area or volume. A foot is 0.3048 m, but a square foot is 0.0929 m² and a cubic foot 0.0283 m³.
- Check which mile. A nautical mile is 1,852 m, about 15 % longer than a statute mile.
Values people look up most
Each one opens the converter with the number already in it.
- 1 mm to cm
- 5 mm to cm
- 10 mm to cm
- 20 mm to cm
- 25 mm to cm
- 30 mm to cm
- 45 mm to cm
- 50 mm to cm
- 75 mm to cm
- 100 mm to cm
- 150 mm to cm
- 200 mm to cm
- 250 mm to cm
- 500 mm to cm
- 1,000 mm to cm
Quick reference
| Millimetres | Centimetres |
|---|---|
| 1 mm | 0.1 cm |
| 10 mm | 1 cm |
| 50 mm | 5 cm |
| 100 mm | 10 cm |
| 250 mm | 25 cm |
| 500 mm | 50 cm |
| 1,000 mm | 100 cm |
Questions people ask
How many mm in a cm?
Exactly 10.
What is 45 mm in cm?
4.5 cm.
Which is used on technical drawings?
Millimetres. Metric engineering drawings are dimensioned in mm by default, with no unit written.