[click the pic to see it larger]
If you know what size you want your box to be, L[length], W[width], H[heigth], use the formulas below to find the size of your pieces and corners.
If you're making a small box, or you're a quilter, you can use 1/4" sewing allowance. If you're using a fabric that frays a lot or you want a bigger or stronger box, you might want a 1/2" sewing allowance. I am used to work with cm and only use 1/4" when quilting, so I usually have 1 cm sewing allawance :) It's not that important, as long as you keep it constant. For garments, however, 1/4" is usually a little to little :)
If you have 1/4" sewing allowance and 1/2" where you attach the zipper.
a = L + H +1/2"
b = H + W + 3/4"
c = H * 0.7 [I have no ideea how one can choose to work in base 8 :) and I barely remember how to multiply in base 8, if so ]
If you're using 1/2" allowance and 1" for the zipper, you'll have:
a = L + H +1"
b = H + W + 1 1/2"
c = H * 0.7
And, of course, if you're lucky like me and live life in metric ...
a = L + H + 2 cm
b = H + W + 3cm
c = H * 0.7
Please let me know if you have any questions. And enjoy your pretty pouches :) Oh, and if you have no ideea what I'm talking about, you might want to have a look at the tutorial here.