Millimeter (mm): The millimeter is equal to one one-thousandth of a meter (0.001 meters). It is frequently used for very precise measurements, such as the thickness of paper or the diameter of small objects.
Nanometer (nm): The nanometer is equal to one one-billionth of a meter (0.000000001 meters). It is used to measure extremely small structures, such as molecules and nanoparticles.