I can't imagine a website that would be capable of doing that... You have to figure in the wheel wells, the angle of the wall behind the rear seat, the trunk lid springs, air space for whatever subs you want. Unless you're just doing a genaric type box... then you're woofer should come with dimensions to make a box. Just use your head and prepare to walk down mathematical memory lane. Always be sure to figure the thickness of the wood into the whole scheme of things. I've heard stupid stupid stories about people who forgot to figure that in, then either the air space was to little or the outside dimensions are to big.
Demmy