This calculator estimates body fat two ways — the US Navy tape method, which uses neck, waist and (for women) hip circumference, and the BMI-based Deurenberg formula, which needs only height, weight and age. Whichever you pick it shows the other as a cross-check, then breaks your weight into fat mass and lean mass, places you in the ACE category ranges, and works out the goal weight you would reach at any target body fat percentage assuming you keep your lean mass. Feed the result into the BMR calculator for a lean-mass-based metabolic rate, or the BMI calculator to see how the two measures differ for your build.
Body Fat Calculator
Body fat from a tape measure or from height and weight alone — plus lean mass and your goal weight at any target percentage.
Tape measurements (cm)
Measure relaxed, not flexed. Waist at the navel for men, at the narrowest point for women. Neck just below the larynx. Take each to the nearest 0.5 cm.
Body fat
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Fat mass—
Lean body mass—
Cross-check (other method)—
BMI—
Category ranges for your sex
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Why body fat beats weight
Two people at the same height and weight can look and function completely differently depending on how much of that weight is fat and how much is muscle, bone, water and organs. Body fat percentage splits the two, which is why it tracks health and fitness far better than the scale or BMI alone. A muscular athlete and a sedentary person can share a BMI of 27 while sitting at 12% and 30% body fat respectively.
The US Navy method
Developed by Hodgdon and Beckett at the Naval Health Research Center in 1984, this estimates body density from circumference measurements and converts it to a fat percentage. Men need height, neck and waist; women also need hip circumference, because women store proportionally more fat around the hips and thighs and the male equation would systematically underread. It needs nothing but a tape measure and lands within roughly 3–4 percentage points of a DEXA scan for most adults.
The BMI method
The Deurenberg formula (1991) estimates body fat from BMI, age and sex: body fat % ≈ 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4, where sex is 1 for men and 0 for women. It requires no tape at all, which makes it useful as a quick check or when travelling, but it inherits BMI's core weakness — it cannot tell muscle from fat, so it overestimates for muscular people and underestimates for those with low muscle mass.
Measuring properly
Technique matters more than the formula. Measure at the same time of day, ideally first thing in the morning before eating. Keep the tape snug but not compressing the skin, and level all the way round. Do not suck in or flex. Take each measurement twice and average them. A centimetre of sloppiness at the waist can shift the result by a full percentage point, which is enough to invent progress that is not there.
What the categories mean
The American Council on Exercise ranges are the usual reference. For men: essential fat 2–5%, athletes 6–13%, fitness 14–17%, average 18–24%, obese 25% and above. For women: essential 10–13%, athletes 14–20%, fitness 21–24%, average 25–31%, obese 32% and above. Women's essential fat is higher for hormonal and reproductive reasons — this is physiology, not a different standard.
Use it as a trend, not a verdict
Every field method carries a few points of error, so the absolute number is less trustworthy than its direction over time. Measure the same way every two to four weeks and watch the trend. If your body fat percentage falls while your weight holds steady, you are recomposing — gaining muscle while losing fat — which the scale alone would have shown as failure. Pair this with the TDEE calculator to set the calorie target that drives the change, and the BMR calculator, where a body fat percentage unlocks the more accurate Katch–McArdle formula.
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Frequently asked questions
How accurate is the US Navy body fat method?
It typically falls within 3–4 percentage points of a DEXA scan for most adults, which is good for a method needing only a tape measure. It is least accurate at the extremes — very muscular or very lean people — and consistency of measurement technique matters more than the formula itself.
Why do women need a hip measurement but men do not?
Women store proportionally more fat around the hips and thighs, a distribution the waist-and-neck measurements alone cannot capture. The female equation adds hip circumference so it does not systematically underestimate. It is a physiological difference, not an arbitrary one.
What is a healthy body fat percentage?
Using ACE ranges, the fitness band is 14–17% for men and 21–24% for women, with the average band running to 24% and 31% respectively. Below roughly 5% for men and 13% for women is essential fat territory, which is not safe to sustain.
Why does my smart scale give a different number?
Bioelectrical impedance scales pass a small current through your body and infer fat from resistance, so they are very sensitive to hydration, food, and recent exercise — readings can swing several points in a day. Tape and impedance methods use entirely different assumptions and will not agree. Pick one and track its trend.
How often should I measure?
Every two to four weeks. Body composition changes slowly, and measurement error is large enough that weekly readings mostly show noise. Measure at the same time of day under the same conditions, ideally in the morning before eating.
Can I lower body fat percentage without losing weight?
Yes — that is body recomposition. Gaining muscle while losing an equal mass of fat keeps the scale flat but drops the percentage. It happens most readily in beginners, people returning after a break, and anyone in a modest deficit with high protein intake and resistance training.