A calculator would be between 100 and 150 millimetres.
The answer will depend on what aspect of the calculator you wish to measure: its length, volume, mass, weight, temperature, etc.
Metres
You would use either inches or centimeters.
I would use centimetres.
You would use a ruler and measure in millimeters or centimeters.
Centimeters
mmeters
Centimetres
centimeter
feet
Millimetre.
Milimeters