Standard Mat and Frame Sizes

I'm doing some research as I prepare to buy mat board for my photography class portfolios...

For a 13x19 print, the standard mat/frame size is 18x24.

For an 8 1/2 x 11 print, the standard mat/frame size is 11x14 or 16x20.

Now, off to decide where to buy mat board from, since my school doesn't sell it cheaply anymore!