A metre.
It would be normal to use either meters or feet, but you can use any unit for length (inches, cm, mm, km, etc.)
Feet would be nice, or meters where the metric system reigns.
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.
Tonnes
tons
Inches
cm
I would use feet
You would use meters.
yards
centimeter