MM to CM Converter
A centimetre is exactly 10 millimetres, so millimetres to centimetres is one division: cm = mm / 10. In decimal that is the point moving one place to the left, which is why 1 mm is 0.1 cm, 10 mm is 1 cm, 25 mm is 2.5 cm and 1,000 mm is 100 cm. Both units are defined from the metre, a millimetre as a thousandth of it and a centimetre as a hundredth, so the ratio is exact. Displayed answers round to twelve significant digits, with very large or small results shown in exponential notation. This page opens the converter with millimetres in the From box and centimetres in the To box, whatever pair you converted last, and lists the same length in metres, kilometres, inches, feet, yards, miles and nautical miles under the answer.
1 mm in every length unit
Common questions
- How many cm is 1 mm?
- 0.1 cm, because ten millimetres make one centimetre. The pattern holds at every size: 5 mm is 0.5 cm, 15 mm is 1.5 cm, 25 mm is 2.5 cm, 150 mm is 15 cm and 12,345 mm is 1,234.5 cm. The mathematical conversion moves the decimal point one place to the left; the displayed result may round longer inputs to twelve significant digits.
- What is the formula for mm to cm?
- Centimetres = millimetres / 10, and millimetres = centimetres × 10 in the other direction. Milli means a thousandth of a metre and centi means a hundredth, so a centimetre is ten millimetres by definition rather than by measurement. The factor is exact, though dividing by ten can add a decimal place and the displayed answer follows the converter's precision limits.
- Do I move the decimal point left or right?
- Left by one place going from millimetres to centimetres: 7 mm becomes 0.7 cm and 340 mm becomes 34 cm. Right by one place going the other way: 7 cm becomes 70 mm. The Swap units button between the two boxes reverses the pair, so this page turns into a centimetres to millimetres converter without a reload.
- Does dividing by 10 also work for square and cubic millimetres?
- No, and this is where the mistake usually happens. Area squares the ratio, so 100 mm² is 1 cm², and volume cubes it, so 1,000 mm³ is 1 cm³, which is also exactly 1 millilitre. For areas, use the Area category chip above the converter and turn on the uncommon units switch, which adds square millimetres next to square centimetres. The Volume category here lists millilitres, litres, cubic metres, cubic inches and cubic feet, not cubic millimetres, so cube the 10 yourself for those.
- What is the same length in inches or feet?
- The list under the answer already has it, because the converter works out every common length unit at once rather than one target at a time. Type 100 in the From box and it reads 10 cm in the headline, 3.93700787402 in for inches, 0.328083989501 ft for feet and 0.1 m for metres. Values in the list are shown to twelve significant digits, and Copy result copies the headline exactly as printed, without the thousands separators.
- Why does the page open on mm and cm when I last converted something else?
- Because a page that names a pair should show that pair. This one sets millimetres and centimetres on arrival, ahead of whatever the converter last remembered, and it leaves the main unit converter's own memory alone: go back there and it is still on the pair you left it on. The number you last typed does come with you, since it is usually the one you are still working on.
Conversion factors are the exact legal definitions where one exists. An inch is exactly 2.54 cm and a pound exactly 0.45359237 kg, so those conversions are exact rather than approximate. Temperature uses offsets rather than factors, and that is shown in the working.