FIRST WAY... Measure through your belt loops on a well fitting pair of pants and pull the tape to your desired snuggness. Tell us the measurement that you get.
SECOND WAY... Measure an old belt. See the picture at left to determine where to start measuring and where to stop. Notice that the starting point is NOT at the end of the belt but where the tongue touches the buckle when a rest. The measurement that you get should be the same measurement that you'd get if you put the tape through your belt loops.
THIRD WAY... Add 2" to your pant waist size. This should also be the measurement that you'd get if you put a tape measure through your belt loop. This measurement is pretty close if you're happy with "pretty close" and works for men... not for women.