The answer depends on what characteristic you wish to measure: its length, width, mass, temperature, reflectivity (albedo), thermal or electrical conductivities, and so on.
Either a ruler or a scale.
inch or centimeter
You should use the "math book" to look up the answer to this question as opposed to just having someone answer it on this website.
in ur head
a math book is were u learn math
the mass of your book has about one killogram how do i no cause im cool
The math book was as heavy as a mountain.
it is a book that teaches math.
The metric (SI) unit for weight is the newton, since weight is a force. When people talk about "weight", they sometimes actually mean "mass". The unit for mass is the kilogram.
bar modeling is math
A unit is 1.
The math unit pi (not pie!) is approx 3.14159 which is 314.159%