I'm used to counting bets from casino play, so I usually multiply the number of bets in the pot by the number of outs I have, divide by the number of bets I have to call, and compare the result to 45 (number of cards remaining) minus the number of outs I have. The number of cards remaining is obviously greater than 45, but there are a few reasons I use this number, and it doesn't affect the calculation that greatly.

Example: There are 7 bets in the pot, I know I am behind and have 6 clean outs, and I have to call one bet. 7x6/1 = 42 > 45-6, so I call. For two bets I would fold.

Sounds convoluted, but it's second nature to me.