1 cm is 10 mm, 1 m is 100 cm, and 1 km is 1000 m. Memorizing the numbers alone can be confusing, but it is much easier to understand when you compare how the same length is expressed as different numbers in different units. Move the slider to change the length and see for yourself.
Conversion rules: To convert mm → cm, divide by 10 (1 cm = 10 mm); to convert cm → m, divide by 100 (1 m = 100 cm); and to convert m → km, divide by 1000 (1 km = 1000 m). To go from a larger unit to a smaller unit, multiply instead.
Tip to avoid confusion: Remember how many places the decimal point moves. For example, when converting cm to m, move the decimal point two places to the left. Then you can convert quickly without a calculator.