Meters or centimeters. Eg. 0.5 m or 50 cm.
The metric unit of length is the 'meter'.
The basic metric unit of measure for length is the meter (m).
I would use centimetres.
mmeters
Centimetres
centimeter
feet
Millimetre.
Milimeters
By unit of length and distance and conversion ,we can say that the most appropriate unit to measure the length of a finger is cm.
You would use a ruler and measure in millimeters or centimeters.
Length->metersVolume->LitersMass->grams