The centimetre (cm) is a unit of length in the metric system, equal to one-hundredth of a meter.
The millimetre (mm) is a unit of length in the metric system, equivalent to one-thousandth of a meter and is the SI base unit of length.
Conversion from cm to mm
Thus, 1 cm is equal to 10 mm.
Hence, to convert the value from cm to mm, multiply the value by 10.
Convert 40 cm to mm
We know that, 1 cm = 10 mm
40 cm = (40 × 10) mm
= 400 mm
Therefore, 40 centimetres is equal to 4000 millimetres, or 40 cm = 400 mm.