how to calculate volume for slanted box?

yes, i've calculated the box to be .655 cubic feet. now next step is figuring out what the angle is that I need to cut the edge of the MDF with so that it's sits flush. does this make sense?

45 degree angle is what I'm guessing. Should be easy if you have a circular saw that can be adjusted for angles.

no, wouldn't be 45 degrees. it's an acute right triangle that is formed. angle would be something like 60 at bottom and 30 at top, but i need to find my old trig equations to get it exactly

Old trig equations? lol. Maybe if you drew a picture it would be a lot easier if you posted it. If I had the dimensions of your box it would be easier. If you are going to cut it at 60 on top and 30 on bottom, just remember the other side has to be whatever it takes to equal 90. Meaning where the two pieces fit together, one is 60 and one is 30. I said 45 degrees becuase you said a slanted box, which made me think you made it have 2 equal sides.

sorry, heres a pic - i just found a trig site though, so I calculated the angles

hm, try this link

dammit this? http://www.hostedimage.com/usr/968/Sub_Box_Measurements.GIF

You actually have a tape measure that measures to the thousandth?