Stand up straight but do not suck in your stomach; be relaxed. Measure your waist at the greatest circumference. Men sometimes have trouble with this measurement. It can vary by five inches quite easily. For example, Covert gets:
Please play around with the measurements a little. Get all five and run them through the formula; you'll find there's quite a variation. You may be tempted to use the results of 1, 2, or 3, but the results of 4 are the most accurate.