by Guest » Sat Mar 19, 2005 7:50 pm
mL and cc (properly cm^3) are measures of volume, and
1 mL = 1 cm^3 exactly by definition.
mg (milligram) is a unit of mass. Different substances have different densities or mass per unit volume. In general you have to know the density of the substance. However, water at 4 degrees C is approximately 1.000 g/mL (there are a few digits to the right if you carry enough decimal dust). Lead is heavier, feathers are lighter.