Length
The spatial extent or distance between two points measured along a specified path.
SI unit
m
In depth
Length is one of the seven fundamental SI base quantities. Since 2019, the meter is defined precisely by fixing the speed of light in vacuum to c = 299,792,458 m/s.
Examples in the real world
Measuring the wavelength of red light (~650 nm), the height of a doorway (~2 m), or astronomical distances like an astronomical unit (~1.496 × 10¹¹ m).