A square nanometer.
Square metre
Square centimetres (cm2).
That one!
Metric ruler
liter
Millimetres
a millimeter
You would use square metres (m2) to find the area of a door.
To find the area of a book cover in metric units, the most appropriate unit to use would be centimeters. The formula for finding the area of a book cover would be: length x width.
Square metre
square meter
Square metres
Square meters.
meters2
Square meters, generally.
Square centimetres (cm2).
Square centimetre.