A ruler or tape measure would commonly be used to measure the width of a book.
You measure it.
With a ruler..... hahaha
Height by width and a ruler. :)
Millimetres
the metric system
You would typically use inches to measure a paperback book. You can measure the length, width, and thickness of the book in inches to determine its size.
It depends on what is being measured. The instruments and units used for measuring the length, width and height of a building would be different to those used for a matchbox!
A centimetre should suffice.
instruments are technically used to enhance are sense to discover new things. Such as a telescope and a microscope.
To measure clints and grikes in a limestone pavement, you can use a tape measure, calipers, or a ruler to measure the width and depth of the features. Additionally, a compass can help determine the orientation of the clints and grikes.
A centimetre, although you could use a millimetre for greater accuracy.
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.