cut the side view into different areas on a sheet of paper. You'll make a square, and a triangle. The square is length time width. The triangle, is 1/2 of the length times the height, since a triangle is only half of a square. Then once you have the area of the side view, multiply it times the width of the box. If the box is for two speakers, dont forget to take off for the two side walls and the center divide. Once you have volume, im sure you know to devide by 1728 and you have cubic feet.
Cool thanks , it was the 1728 that I forgot ...Anyone that wants to help design this box , I am open to designs , Would kinda like one 10 behind passenger seat and the other kinda in the middle so that I can mount the amp behind my seat and not loose no clicks , unless the box is thin enough . The prefab boxes I loose like 3 clicks or more and I am a tall man , so that is bad ..lol