The unit of length is expressed in letters, that is, meter pm, trillion meter mm, kilometer km, decimeter dm, centimeter cm, millimeter Mm, silk meter dmm, millet cmm, micron micron, nanometer nm, picometer Pm, femtometer fm, amiam, etc.

The unit of length refers to the basic unit for measuring spatial distance, which is formulated by human beings to standardize the length. Its international unit is "meter" (symbol "m"), and commonly used units are millimeter (mm), centimeter (cm), decimeter (dm), kilometer (km), meter (m), micron (micron) and nanometer (nm). Length units play an important role in various fields.