I think with some relatively simple math you'll be able to calculate the amount of stars

First surface of a sphere:

For pumped stars you need the *inner* sphere you will create when putting in the pumped stars.

Say the inner diameter of your 6" hemi is 5,25 inches and your pumped stars are 1/2 inch.

Your *inner* sphere diameter is: 5,25 - (2 * 1/2) = 4,25

The formula for the surface of a sphere is 4πr

^{2} so:

4 * π * (4,25/2)

^{2} = 86,6 which would mean ~346 square 1/2" stars (optimum).

This will tell you that the factor for nice circle packing is ~ 0.907 so:

346 * 0.907 =~ 314 pumped 'round-square' 1/2" stars.

Volume cylinder: πr

^{2}*h so one (1) of your pumped stars has a volume of π(1/4)

^{2}*(1/2) =~ 0,0982

^{2} inch.

So total volume of the stars: 314 * 0.0982 =~ 30,8

^{2} inch.

Only thing you have to know now is the density of your comp in these stars. I you have some left overs weigh them, or do a dry pump etc..

**Edit**: The math needed for a 100% accurate calculation is much more complex but does not make a better prediction.

**Edited by pdfbq, 06 May 2012 - 05:59 AM.**