What is the standard unit of length?

The standard SI unit of length is the meter. It is defined as the distance traveled by light in a vacuum during 1/299,792,458th of a second.

The meter is the chosen International System of Units or SI unit for length. It is part of the metric system that is used internationally for scientific, commercial and other purposes. In the United States, two measurement systems, the SI and U.S. Customary System, exist. The foot is the unit for length in the U.S. Customary System. This unit is used mainly for commercial purposes. One foot, or 12 inches, is equivalent to 0.3048 meters, or 30.48 centimeters.