here's how you do it:
put his made hands into pokerstove
get your equity vs. his made hands

if it's enough then it doesn't matter
if it's not enough, then calculate what % of the time he has to be bluffing for you to make money on the call

so say you need 33% equity to make a pot sized call
say pokerstove gives you 20% equity vs. his value range

that means that he has to have his value range 83% of the time and air 17% of the time
.83 * .2 = 0.166 (20% equity vs. value)
.17 * 1 = 0.17 (100% equity vs. air)
total chance of winning the hand is 33.6%

if he bluffs less than 17% we will lose, if he bluffs more we will make money