4 cm on a ruler is equal to 40 millimeters on the ruler.
Every cm is equal to 10 millimeters.
Each centimeter is equal to 10 millimeters, so if your object measures 4 centimeters long, that's equivalent to 4 × 10 = 40 millimeters. Often, your measurement in millimeters will fall between centimeter marks on the ruler.
Also there are 2.54 cm in every inch of measurement.
And in 4 cm there are 1.5748 inches in the 4 cm.
A centimeter (cm) is a decimal fraction of the meter, the International System of Units (SI) unit of length, approximately equivalent to 39.37 inches.
In 1 foot there are 30.48 cm and in 2 feet there are 60.96 cm.