Guide for the Use of the International System of Units (SI)

8.2 Volume 
 
The SI unit of volume is the cubic meter (m
3
) and may be used to express the volume of any 
substance, whether solid, liquid, or gas. The liter (L) is a special name for the cubic decimeter (dm
3
), but 
the CGPM recommends that the liter not be used to give the results of high accuracy measurements of 
volumes [1, 2]. Also, it is not common practice to use the liter to express the volumes of solids nor to use 
multiples of the liter such as the kiloliter (kL) [see Sec. 6.2.8, and also Table 6, footnote (b)]. 
 
8.3 Weight 
In science and technology, the weight of a body in a particular reference frame is defined as the 
force that gives the body an acceleration equal to the local acceleration of free fall in that reference frame 
[4: ISO 80000-4]. Thus the SI unit of the quantity weight defined in this way is the newton (N). When the 
reference frame is a celestial object, Earth for example, the weight of a body is commonly called the local 
force of gravity on the body.
Example: The local force of gravity on a copper sphere of mass 10 kg located on the surface of the 
Earth, which is its weight at that location, is approximately 98 N. 
Note: The local force of gravity on a body, that is, its weight, consists of the resultant of all the 
gravitational forces acting on the body and the local centrifugal force due to the rotation of the 
celestial object. The effect of atmospheric buoyancy is usually excluded, and thus the weight of a 
body is generally the local force of gravity on the body in vacuum. 
In commercial and everyday use, and especially in common parlance, weight is usually used as a 
synonym for mass. Thus the SI unit of the quantity weight used in this sense is the kilogram (kg) and the 
verb “to weigh” means “to determine the mass of” or “to have a mass of.”
Examples: the child’s weight is 23 kg 
the briefcase weighs 6 kg 
Net wt. 227 g 

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