Inches or centimetres are fine for a book's dimensions. Measure the width, height and depth to determine the volume.
If you are talking about the length of the book's narrative, word count is probably the most accurate.
Time
meeters?
a millimeter
Millimetre.
The meter.
Cm .
A kilometre.
Centimeters
Centimeters
Millimetre.
a millimeter
Time
meeters?
Milligrams
Kilometres
Inches, millimetres or centimetres.
the metric system