For two bodies having masses m and M with a distance R between their centers of mass, the equation for Newton’s universal law of gravitation is 
F = G mM /R2,
where F is the magnitude of the gravitational force and G is a proportionality factor called the universal gravitational constant.  
G is a universal gravitational constant—that is, it is thought to be the same everywhere in the universe.  
It has been measured experimentally to be
 
G = 6.674×10−11N⋅m2  / kg2
 
in SI units.  
 
Note that the units of G are such that a force in newtons is obtained from F = G mM /R2, when considering masses in kilograms and distance in meters. 
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