Body Fat Calculator: US Navy Tape Method

Estimate your body fat percentage with a tape measure in two minutes. This free calculator uses the US Navy circumference method to show your body fat, fat mass, lean mass and where you sit on the American Council on Exercise body fat chart.

Just below the Adam’s apple, tape sloping slightly down at the front.

Men: around the belly at navel level, after a normal breath out.

Your estimated body fat
0%
0%15%30%45%
0fat mass
0lean mass (everything else)
–ACE category

Body fat categories (American Council on Exercise)

Category Men
Every body fat estimate has error. Tape methods, smart scales and even lab scans can disagree by several percentage points. Measure the same way, at the same time of day, every 2–4 weeks and watch the trend, not one number.
Check with your doctor if you are losing weight without trying, or if you have a history of eating disorders. Very low body fat can harm hormones, recovery and bone health.

How this body fat calculator works

It uses the US Navy circumference equations developed by Hodgdon and Beckett at the Naval Health Research Center (1984). For men, body density is predicted from waist minus neck and height. For women, it uses waist plus hips minus neck and height. Body density is then turned into body fat percentage with the classic Siri equation (495 ÷ density − 450). Fat mass is your weight times your body fat percentage, and lean mass is everything else: muscle, bone, organs and water.

The category comes from the general body fat chart published by the American Council on Exercise (ACE): essential fat, athletes, fitness, average and obese. These are broad guides, not health verdicts.

How to measure for the best result

  • Use a flexible tape, snug on the skin but not squeezing it, and keep it level.
  • Measure in the morning before eating, standing relaxed, after a normal breath out.
  • Take each measurement twice. If they differ by more than 1 cm (about half an inch), measure a third time and use the average.
  • Men measure the waist at the navel. Women measure the waist at its narrowest point and the hips at the widest part of the buttocks.

What to do with your number

If your body fat is in the average or higher range, the goal after 35 is to lose fat while keeping every bit of muscle you can: lift weights 2–4 times a week, eat enough protein, and use a moderate calorie deficit. The calculator shows what you would weigh at the top of the ACE fitness range if you kept all your current lean mass. That is a more useful target than a random number on the scale. Read how to lose fat and keep muscle after 35, why BMI vs body fat tells you different things, and how much protein you need after 35.

Sources

  1. Hodgdon JA, Beckett MB (1984). Prediction of percent body fat for U.S. Navy men from body circumferences and height. Naval Health Research Center Report 84-11
  2. Hodgdon JA, Beckett MB (1984). Prediction of percent body fat for U.S. Navy women from body circumferences and height. Naval Health Research Center Report 84-29
  3. Siri WE (1961). Body composition from fluid spaces and density: analysis of methods. In: Techniques for Measuring Body Composition. National Academy of Sciences.
  4. American Council on Exercise (ACE): general body fat percentage categories for men and women.

This calculator gives general education, not medical advice. It cannot diagnose any condition. Talk to your doctor before making big changes to your diet or training, especially if you have a health condition.

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