Body fat calculator
Estimate your body fat percentage from a few tape measurements. Choose the US Navy method (neck, waist and, for women, hips) or the newer one-site Army equation (waist and weight). Both are free, take a minute, and need nothing more than a soft tape measure.
How to measure (the part that decides accuracy)
Use a soft tape, stand relaxed, and breathe out normally before you read the number. Don't pull the tape so tight it presses into the skin. Measure twice and use the average.
Neck: just below the larynx (Adam's apple), with the tape sloping slightly down to the front. Waist for the Navy method: men at the navel, women at the narrowest point of the torso. Waist for the one-site method: at the navel for everyone. Hips (women, Navy method): around the widest part of the buttocks.
Measure in the morning, before eating, and on the same day of the week. Water, food and bloating can move a waist measurement by a centimetre or more, and that alone moves the result.
The formulas behind the calculator
The Navy method comes from Hodgdon and Beckett's work at the Naval Health Research Center in 1984. It uses height and the difference between waist and neck (plus hips for women), because a thicker waist relative to the neck tracks body fat closely. All US military services adopted these equations in 2002.
In 2023 the US Army moved to a one-site tape test that uses only the abdominal circumference and body weight. This calculator uses the one-site equation published by Army researchers (Taylor and colleagues, 2024), which was built and validated against DXA scans in active-duty soldiers. The Army's official scoring may differ slightly.
The categories (essential, athletic, fitness, average, above average) follow the widely used American Council on Exercise chart. They describe typical ranges, not health limits.
How accurate is a tape-measure body fat estimate?
For most people, circumference equations land within roughly 3–4 percentage points of a lab method like DXA. They work less well at the extremes: very lean, very muscular, or carrying a lot of abdominal fat. Two people with the same numbers can have different body compositions.
That doesn't make the number useless. Measured the same way every time, the trend is far more reliable than any single reading. If your estimate drops from 24% to 21% over three months, the direction is real even if the exact value is off by a couple of points.
Skip the tape: get it from two photos
Trainr estimates body fat and body measurements from a front and a side photo, then tracks them week after week — so you see whether you're losing fat or muscle, not just weight. The first scan is free.
Scan yourself — the first one is freeCommon questions
What is a healthy body fat percentage?
On the ACE chart, the 'fitness' range is 14–17% for men and 21–24% for women, and 'average' is 18–24% for men and 25–31% for women. Essential fat — the minimum the body needs — is about 2–5% for men and 10–13% for women.
Navy or one-site: which method should I use?
If you can measure your neck reliably, the Navy method uses more information. The one-site method is quicker and less sensitive to how the neck is measured. Pick one and stick with it — switching methods makes the trend meaningless.
Why is my result different from my smart scale?
Bioimpedance scales estimate body fat from an electrical signal that changes with hydration, so they can swing several points in a day. Tape methods use shape instead. Neither is a lab measurement; consistency matters more than the device.
Can I calculate body fat without calipers?
Yes. That's what this calculator does: it uses circumferences from a tape measure, not skinfolds. You only need a soft tape and a scale for the one-site method.
How often should I measure?
Every one to two weeks is enough. Body fat changes slowly, and measuring daily mostly captures water and food.
One reading is an estimate. The same measurement repeated every couple of weeks is a trend you can trust.
Sources
- Hodgdon JA, Beckett MB (1984). Prediction of percent body fat for U.S. Navy men and women from body circumferences and height. Naval Health Research Center, Reports 84-11 and 84-29.
- Taylor KM, Castellani MP, Bartlett PM, et al. (2024). Development and cross-validation of a circumference-based predictive equation to estimate body fat in an active population. Obesity Science & Practice. https://pmc.ncbi.nlm.nih.gov/articles/PMC11026907/
- American Council on Exercise. Percent body fat calculator and norms. https://www.acefitness.org/resources/everyone/tools-calculators/percent-body-fat-calculator/
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Trainr is a wellness tool, not a medical device. These calculators give estimates for self-tracking, not a diagnosis. For medical questions, talk to a professional.