Estimate your body fat with a tape measure, using the US Navy method.
The US Navy developed this method to estimate body fat quickly with nothing more than a tape measure. It's based on the work of Hodgdon and Beckett at the Naval Health Research Center, who compared circumference measurements with underwater weighing, and it's still used for military fitness standards today.
The formulas use inches:
Metric measurements are converted to inches first, so you get the same answer either way.
The colored scale uses the American Council on Exercise categories: essential fat, athletic, fit, average, and above average. Add your weight to see how much of it is fat and how much is lean mass, along with your FFMI (fat-free mass index), a measure of how much muscle you carry for your height.
Your body fat percentage makes other calculators more accurate. The links under your results pass it straight into the Ideal Weight Calculator for Lifters (to see your weight at a leaner body fat with the muscle you have) and the Calorie Calculator (which can then use the Katch-McArdle formula). Wondering how much muscle you could build? Try the maximum muscular potential calculator.
Any home method has error. What makes the tape useful is that the error stays about the same if you measure the same way. Measure every two to four weeks, at the same time of day, and watch the direction. A waist going down while your lifts go up (logged in GymGod or anywhere else) is the clearest sign you're losing fat, not muscle.
For most people it lands within about 3–4 percentage points of a lab measurement such as a DEXA scan. It's less accurate for very lean, very muscular, or very heavy people, because it only looks at a few circumferences. Its real strength is consistency: measured the same way each time, it tracks change well.
Men: neck just below the Adam's apple, waist at the navel. Women: neck just below the larynx, waist at its narrowest point, hips at their widest. Stand relaxed, don't suck in, keep the tape level and snug without compressing the skin. Measure two or three times and use the average.
The American Council on Exercise lists 14–24% as fit-to-average for men and 21–31% for women. Athletes are often leaner: about 6–13% for men and 14–20% for women. Going much below that, especially below essential fat levels, isn't healthy long term.
Most people store a large share of their fat around the waist, so waist size changes closely track body fat changes. That's why the Navy method, and many health guidelines, focus on it.
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GymGod logs your workouts and bodyweight together, so you can see whether the scale is moving for the right reasons.
