Body fat percentage tells you what BMI cannot: how much of your weight is fat and how much is everything else. This calculator uses the US Navy circumference method, which needs nothing but a tape measure and is accurate to within about 3–4 percentage points of a DEXA scan for most people.
- What it measures
- Proportion of body weight that is fat
- Method
- US Navy circumference (Hodgdon & Beckett)
- Equipment
- A flexible tape measure
- Typical accuracy
- ±3–4 percentage points vs DEXA
- Healthy range
- 14–24% men · 21–31% women
Formula
US Navy circumference method (Hodgdon & Beckett, 1984)Men: %BF = 495 ÷ (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450 Women: %BF = 495 ÷ (1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.22100 × log₁₀(height)) − 450
- waist
- — Waist circumference in centimetres
- neck
- — Neck circumference in centimetres
- hip
- — Hip circumference in centimetres (women only)
- height
- — Standing height in centimetres
The equations are different for men and women because fat distribution differs — the female version includes hip circumference, the male version does not. Both are the metric form; the imperial version published by the Navy gives the same answer.
Body Fat Calculator examples
| Input | Result | Category |
|---|---|---|
| Man, 5'10", 180 lb, 35" waist | 18.4 % | Average |
| Man, 5'10", 200 lb, 38" waist | 22.9 % | Average |
| Man, 6'0", 190 lb, 34" waist | 14.6 % | Fitness |
| Woman, 5'5", 150 lb, 30" waist | 29.5 % | Average |
| Woman, 5'5", 130 lb, 27" waist | 23.7 % | Fitness |
| Woman, 5'7", 165 lb, 32" waist | 32.5 % | Above average |
How do I measure for this calculator?
The result is only as good as the tape work. Measure on bare skin, keep the tape snug but not compressing, and take each measurement twice — if the two differ by more than half an inch, measure again.
- 1.Neck — just below the larynx, with the tape sloping slightly downward at the front. Do not flare your shoulders.
- 2.Waist (men) — at the navel, horizontal all the way round.
- 3.Waist (women) — at the narrowest point of the torso, usually just above the navel.
- 4.Hips (women) — at the widest point of the buttocks, feet together.
- 5.Measure at the end of a normal exhale, standing relaxed. Do not suck in.
What is a healthy body fat percentage?
Women naturally carry substantially more essential fat than men — roughly 10–13% versus 2–5% — because of reproductive and hormonal requirements. Any comparison across sexes without accounting for that is meaningless.
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Obese | 25% and above | 32% and above |
Sitting in the 'average' band is not a problem in itself. The health signal comes at the extremes: below essential fat impairs hormone production, immune function, and in women menstrual regularity, while the obese band carries the metabolic risks usually attributed to high BMI.
How accurate is the Navy method?
Validation studies put the standard error at roughly 3–4 percentage points against hydrostatic weighing or DEXA. In practice that means a result of 22% should be read as 'somewhere between about 18% and 26%' rather than as a precise figure.
It is least accurate at the extremes — very lean and very obese people — and for anyone whose fat distribution is unusual for their sex, since the equation infers whole-body composition from a couple of circumferences.
Its real strength is consistency. Because the same tape positions produce the same systematic error every time, the method tracks change reliably even when the absolute number is off. A drop from 24% to 20% over three months is trustworthy even if your true values were 27% and 23%.
Why does the BMI estimate differ from the tape estimate?
The second figure shown alongside your result uses the Deurenberg equation, which predicts body fat from BMI, age, and sex alone. It knows nothing about your shape.
When the two disagree by a wide margin, that gap is the interesting result. A tape estimate well below the BMI estimate means you carry more muscle than the population average for your weight. A tape estimate well above it usually means the opposite — sometimes called normal-weight obesity, where BMI looks fine but body composition does not.
Body fat versus BMI
BMI is faster and needs no tape, but it cannot separate muscle from fat. Body fat percentage answers the question BMI only approximates, which is why a muscular athlete can be 'obese' by BMI and athletic by body fat.
Neither replaces waist circumference for cardiometabolic risk specifically. Visceral fat around the organs drives that risk, and a waist over 40 inches in men or 35 inches in women flags it regardless of what either percentage says.
Frequently asked questions
How accurate is the Navy body fat calculator?
It estimates body fat to within about 3–4 percentage points of a DEXA scan for most people. That is good enough to place you in a category and to track change over time, but not precise enough to treat a single reading as an exact figure.
Why does the calculator ask for my neck measurement?
Neck circumference acts as a proxy for frame size and lean tissue. Subtracting it from the waist isolates the portion of abdominal girth attributable to fat rather than to skeletal build, which is what makes the equation work across body sizes.
What is a good body fat percentage for abs to show?
Visible abdominal definition typically appears around 10–12% in men and 18–20% in women, though it varies with genetics and fat distribution. Sustaining levels much below that is difficult and, for women, can disrupt menstrual function.
Can I lose fat without losing weight?
Yes. Gaining muscle while losing fat keeps scale weight flat as body composition improves — which is exactly the situation BMI misreads. Tracking body fat percentage and waist circumference catches progress that the scale hides.
Should men and women use different body fat targets?
Yes, and the difference is large. Women require roughly 10–13% essential body fat compared with 2–5% for men, so every healthy range sits about 8–10 percentage points higher for women. Applying male targets to women is harmful.
How often should I remeasure?
Every two to four weeks is enough. Body composition changes slowly, and day-to-day variation in waist measurement from food, salt, and hydration is large enough to swamp real change over shorter intervals.
Sources
- Prediction of percent body fat for U.S. Navy men and women from body circumferences and height — Naval Health Research Center (Hodgdon & Beckett), 1984
- Body mass index as a measure of body fatness: age- and sex-specific prediction formulas — Deurenberg et al., British Journal of Nutrition, 1991
- Percent Body Fat Norms — American Council on Exercise, 2023
- Assessing Your Weight and Health Risk — waist circumference — National Heart, Lung, and Blood Institute