Which of these units of measurement is the smallest?

Here, the millimeter (mm) is the smallest unit of measure. In order from smallest to largest, they rank: millimeter (mm), centimeter (cm), decimeter (dm), and meter (m). These are all common units of length in the metric system, which is a decimal measuring system. It is a system based on the meter, liter, and gram as units of length, capacity, and weight or mass.

A millimeter is one-thousandth of a meter. A centimeter is one-hundredth of a meter. A decimeter is one-tenth of a meter. The metric system was created about 200 years ago by French scientists who wanted to simplify measurements. Every measurement unit is a factor of ten smaller or larger than the closest other measurement unit. This makes it easy to convert between different metric units of measurement.