The relative density of a green coffee is expressed in gr/ml. This measurement is ‘relative’ because it considers the air space between the beans when calculating - important because the size of the bean will always influence the relative density.
This is very useful for a roaster as it provides a lot of information on how to approach the roast profile. Higher density beans need more heat at the start of the roast, and usually crack harder. There is no ‘acceptable’ or ‘ideal’ range for the relative density, because it should simply never change. If it does, you may have a very big moisture problem.
Weight (g) ÷ Volume (mL) = Density (g/mL)