Volume of trapezoid prism.

V = h(a+b) * L

h = total length
a = area of face a (one of the ends (not top or bottom) = (width of large face * depth)
b = area of other face b = (width of small face * depth)
L = depth

Put that puppy into Excel and vary your different measurements in 3 columns with the formula reading from the columns. You'll get a range of volumes. Oh yeah, make sure all measurements are in the same units.

I think that's got it.