A centimeter is about the width of a fingernail
Millimetres.
ruler
The estimating unit of measurement in question is the millimeter, or mm.
None! I would measure in centimeters if I were you!
1/2 millimeter
about 1 centimeter
about the width of the tip of your fore finger, depending on how wide your fingers are.
Millimeters
centimeters
Mm
appropriate unit to measure the width of a textbook = ce ntimeters
It is any linear unit you want to use, depending on the magnitude of the width and on your particular requirements.