Most likely, you would use millimeters (could use centimeters).
The metric unit of length is the 'meter'.
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.
Length->metersVolume->LitersMass->grams
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