- How many millimeters are in a centimeter?
- Exactly 10. Both units come from the meter: "centi" means a hundredth and "milli" means a thousandth, so a centimeter is 0.01 m and a millimeter is 0.001 m. Ten thousandths make a hundredth, which is why 1 cm = 10 mm with no rounding anywhere, unlike inches to centimeters.
- How do I convert cm to mm without a calculator?
- Move the decimal point one place to the right. 4.5 cm becomes 45 mm, 0.8 cm becomes 8 mm, and 30 cm becomes 300 mm (add a zero when there's no decimal point to move). The common slip is moving it two places, which gives 450 mm for 4.5 cm. If the answer looks ten times too big to fit in your hand, that's what happened.
- How do I read centimeters and millimeters on a ruler?
- The numbered long lines are centimeters. Between each pair are nine short ticks, one per millimeter, and the tick in the middle is usually a little longer to mark 5 mm. To find 12.7 cm, go to the line labeled 12, then count seven ticks past it. That's what the ruler reading in this tool gives you: 12.7 cm reads 12 cm 7 mm.
- Why do some converters show 1.13 cm as 11.299999999999999 mm?
- Computers store decimals in binary, and 1.13 can't be written exactly in binary, the same way 1/3 can't be written exactly in decimal. Multiply it by 10 and a tiny error shows up in the last digits. The length didn't change; the arithmetic just leaks. This tool trims that noise to 15 significant digits, so you get 11.3 mm, which is the answer you'd get with pencil and paper.
- Why do engineers and makers use millimeters instead of centimeters?
- Millimeters let you write most dimensions as whole numbers. A metric engineering drawing lists 127.5 instead of 12.75 cm, and the convention is to dimension everything in millimeters so no one has to check which unit a number is in. Screws follow it too: an M6 bolt is 6 mm across, and A4 paper is 210 × 297 mm. Centimeters stay common for everyday things like clothing sizes, a child's height, or furniture listings.
- How do I convert square or cubic centimeters to millimeters?
- Not with a 10. A square centimeter is 10 mm on each side, so 1 cm² = 10 × 10 = 100 mm². A cubic centimeter is 10 × 10 × 10 = 1,000 mm³. A 3 cm² label is 300 mm², not 30. For volume, note that 1 cm³ is also exactly 1 milliliter, which is why syringe doses in "cc" read the same in mL.
- How do I go the other way, mm to cm?
- Divide by 10, which moves the decimal point one place to the left: 85 mm is 8.5 cm, and 6 mm is 0.6 cm. A bank card, 85.60 × 53.98 mm under ISO/IEC 7810, is 8.56 × 5.398 cm. If your millimeters need to become inches instead, use the mm to Inches Converter.
- Why is rain measured in millimeters?
- Because 1 mm of rain means 1 liter of water fell on every square meter, which makes the number easy to use for gutters, drainage, and gardens. Forecasts in centimeters would put most days' rain after a decimal point. 2.5 cm of rain is 25 mm, which is 25 liters on each square meter of roof.
- Is what I type saved or sent anywhere?
- No. The conversion runs in your browser. Nothing is sent to a server or stored, and closing the tab clears it.
