The coulomb per meter cubed (symbolized C · m -3 ) is the unit of electric charge density. Reduced to base units in the International System of Units ( SI ), 1 C · m -3 is equivalent to one ampere second per meter cubed (1 A · s · m -3 ).
Suppose there is a globe having volume of one meter cubed, and it is supplied with one coulomb of charge with respect to electrical ground. Then the average charge density in the globe is 1 C · m -3 . The local charge density might not be uniform throughout the globe, but might instead be concentrated near the surface, especially if the charge is comprised of an excess of electron s (that is, a negative charge). This is because particles of like charge tend to repel each other. In that case, the local charge density near the center of the globe will be less than 1 C · m -3 , and the local charge density near the surface will be greater than 1 C · m -3 .
If the charge on the globe is doubled, then the average charge density will become 2 C · m -3 . If the diameter of the globe is cut in half while the charge remains the same, then the average charge density will increase by a factor of 8, because the volume will become 1/8 (1/2 3 ) as great as before.