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, select Area and choose Square millimeter and Square centimeter in the menus. Show 1 more controls the uncommon square-millimeter readout row; it does not control menu availability, and the selected source unit is not repeated in the readout. 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 readout works out the same original length in every common unit. A supplied 100 mm is exactly 10 cm and 0.1 m, with 3.93700787402 in and 0.328083989501 ft displayed under the international-inch and foot definitions. Decimal-rational arithmetic preserves the input and exact factors before display rounding. Copy result copies the displayed headline without digit-grouping commas; each visible conversion row has its own Copy button. Displayed and copied values round to twelve significant digits. If native copying fails, a complete selectable summary identifies the input, selected pair and conventions and includes every unit in the category, including uncommon units.

Why does the page open on mm and cm when I last converted something else?

This focused page opens on Millimeter and Centimeter, while preserving the main converter’s saved unit pair. When storage is usable, a saved value and uncommon-unit preference can travel between pages. Its suffix must still match From. Valid deliberate scalar edits can save those fields after a short delay; invalid or incomplete drafts preserve the saved record. Unusable or conflicting records remain until you use Forget saved settings, which keeps the current conversion on screen. Your input and converted values are calculated in the browser and are not uploaded by the converter. The definitions arrive with the page, so conversion needs no external data lookup and keeps working offline after the page has loaded. The core conversion needs no account.

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.

From

To0.1

Category: Length

Base unit: meter

Uncommon units: Show 7 more

Feet, yards and miles use international definitions. A light year uses a 365.25-day Julian year; the parsec coefficient is approximate.

Results round to 12 significant digits using the listed unit definitions. Input must have a finite numeric magnitude and at most 512 significant digits. Type a single decimal or scientific number; a matching From unit suffix is accepted. Commas and grouped spaces separate thousands; decimal commas, fractions and compound measurements are refused.

1 mm in every length unit

Centimetercm
0.1
Meterm
0.001
Kilometerkm
0.000001
Inchin
0.0393700787402
Footft
0.00328083989501
Yardyd
0.00109361329834
Milemi
6.21371192237e-7
Nautical milenmi
5.39956803456e-7

Selectable complete conversion

Unit Converter — Length
Input: 1 (Millimeter, mm)
Result: 0.1 cm (Centimeter)
Displayed values round to 12 significant digits.
Feet, yards and miles use international definitions. A light year uses a 365.25-day Julian year; the parsec coefficient is approximate.
All other units:
Nanometer (nm): 1000000
Micrometer (µm): 1000
Centimeter (cm): 0.1
Meter (m): 0.001
Kilometer (km): 0.000001
Inch (in): 0.0393700787402
Foot (ft): 0.00328083989501
Yard (yd): 0.00109361329834
Mile (mi): 6.21371192237e-7
Nautical mile (nmi): 5.39956803456e-7
Thou (mil): 39.3700787402
Furlong (fur): 0.0000049709695379
Astronomical unit (AU): 6.68458712227e-15
Light year (ly): 1.05700083402e-19
Parsec (pc): 3.24077928944e-20

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, select Area and choose Square millimeter and Square centimeter in the menus. Show 1 more controls the uncommon square-millimeter readout row; it does not control menu availability, and the selected source unit is not repeated in the readout. 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 readout works out the same original length in every common unit. A supplied 100 mm is exactly 10 cm and 0.1 m, with 3.93700787402 in and 0.328083989501 ft displayed under the international-inch and foot definitions. Decimal-rational arithmetic preserves the input and exact factors before display rounding. Copy result copies the displayed headline without digit-grouping commas; each visible conversion row has its own Copy button. Displayed and copied values round to twelve significant digits. If native copying fails, a complete selectable summary identifies the input, selected pair and conventions and includes every unit in the category, including uncommon units.
Why does the page open on mm and cm when I last converted something else?: This focused page opens on Millimeter and Centimeter, while preserving the main converter’s saved unit pair. When storage is usable, a saved value and uncommon-unit preference can travel between pages. Its suffix must still match From. Valid deliberate scalar edits can save those fields after a short delay; invalid or incomplete drafts preserve the saved record. Unusable or conflicting records remain until you use Forget saved settings, which keeps the current conversion on screen. Your input and converted values are calculated in the browser and are not uploaded by the converter. The definitions arrive with the page, so conversion needs no external data lookup and keeps working offline after the page has loaded. The core conversion needs no account.

Results round to 12 significant digits using the listed unit conventions. Many factors are exact definitions; psi and parsec use rounded coefficients. Temperature includes scale offsets. Days and weeks are fixed-duration units, and unit conversion does not determine calendar dates, ambient pressure or a software label’s convention.