Calculating Volume

Hey guys, I am new to this forum, and am starting to do my research to build some custom subwoofer enclosures for a 2004 Honda civic out of fiberglass.  I have read tons of posts here about fiberglassing that have really helped.  My only question I have right now, is what is the easiest way to calculate the volume of an extremely odd shaped box?  I'm not sure how many subs I will use yet, but I know the box will not be square or anything like that.  I read that someone suggested building the box and then filling it up w/ water or something else to calculate volume, but I want to know the volume before I build.  Thanks in advance!

Try splitting your odd shap box into smaller easier to calculate sections.  You have on large rectangular box, easy to measure, and a bunch of smaller boxes or pyramids, add the volumes together and come up with your total.  Not the fastest way, but it will work.  ( Reminds me of  calculas.)

I usually use a box made of cardboard and just look at it where the glass box will be and eye it out then mark with tape. I guess u would have to be kinda artistic or something to do this but all my volumes always come out great. Its always better to make it to big, its a ton easier to add volume than take it away (fiberfill but i dont like it)dream it, build it, fiberglass it