The Planck length
Well the SI unit of length is the meter, and SI is the first standard measurement system...
The meter is used to measure length.
meter, inch, yard
The cubit was a unit of measurement for length
Cubic unit means the measurement of objects using height, length, and width. It is a unit of measurement used for capacity or volume.
Any unit can be used, but the most practical would be yards (for standard measurement) or meters (for metric measurement).
Metres (meters), yards, feet.
It depends on what you are measuring but feet and inches are mostly used.