It depends on ewhat attribute of the thumb you wish to measure:
Some attributes of possible interest are length, mass, conductivity, tensile strength.
If length, probably centimetre. Millimetre or smaller if you wanted an absurd degree of precision.
You would use area. I would use the meter2. Okay
You would use Volume.
You would use either inches or centimeters.
I would use centimetres and millimetres
Honestly you could use any unit of measure! I would use inches. Thanks Cheezpuffz
You would use the unit of measure called "kilograms" to measure the mass of an elephant.
Which unit would you use to measure the water in a full tub?
I would use feet
You would use meters.
You would typically use a unit of weight, such as grams or ounces, to measure a cherry.
You would use area. I would use the meter2. Okay
The Unit Used To Measure A Train Can Be Kilometer.
You would typically use the metric unit of centimeters to measure the growth of your hair.
if i were you , i would use kg
You would use Volume.
to measure a small trashcan
miles