Look at the table for some common metric prefixes and their meanings. You have probably measured lengths or distances many times. The meter is the SI unit used to measure length. A baseball bat is about one meter long. When measuring smaller lengths, the meter is divided into smaller units called centimeters and millimeters.
Most metric rulers have lines indicating centimeters and millimeters.
The centimeter lines are the longer, numbered lines, and the shorter lines are millimeter lines. When using a metric ruler, line up the 0-centimeter mark with the end of the object being measured, and read the number of the unit where the object ends, in this instance 7.5 cm. Surface Area Units of length are also used to measure surface area. A square that's one meter long on each side has a surface area of one square meter. The surface area of an object is determined by multiplying the length times the width.