5x7 = 13
8x10 = 30
7x17 = 9

Just returned from a week long trip to Maine. Nothing but photography for 5 solid days. Never used more than 6 7x17 holders in a day (I expose 2 negatives per setup). I'm sure if I had more, I'd have shot more, but I was always aware that I wanted to have a few holders available just in case I ran across a "Moonrise" or something...