What unit of measurement describes an objects length?

Answer 1

There are many units:

ell, en, em, inch, hand, foot, cubit, yard, fathom, chain, furlong, mile are some Imperial and extinct measures.

The metre with all its prefices (yotta, zetta, exa, peta, tera, giga, mega, kilo, hecto, deca, deci, centi, milli, micro, nano, pico, femto, atto, zepto, yocto) are SI units along with special ones such as Angstrom.

Then there are astronomical units such as the Astronomical Unit (average Earth-Sun distance), parsec, light year.

And there is the Planck length, the smallest measurable length.