Body Fat Calculator
Estimate your body fat percentage from four tape measurements using the US Navy method, then cross-check it against the Deurenberg BMI equation. Shows lean mass, fat mass, your ACE category, and how far the estimate can reasonably be off.
Mass composition
- Fat mass
- 12.3 kg
- Lean mass
- 62.7 kg
Cross-check
- BMI
- 23.7
- BMI method (Deurenberg)
- 19.1%
Reference target for your age
- Jackson & Pollock reference
- 12.7%
- Fat to lose to reach it
- 3.2 kg
Body fat categories (ACE)
Classifications published by the American Council on Exercise. Women carry more essential fat than men, so every band sits higher.
| 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%+ | 32%+ |
Reference body fat by age (Jackson & Pollock)
These reference percentages rise with age because fat-free mass declines over time. They describe a healthy mid-range, not a goal you must hit.
| Age | Men | Women |
|---|---|---|
| 20–24 | 8.5% | 17.7% |
| 25–29 | 10.5% | 18.4% |
| 30–34 | 12.7% | 19.3% |
| 35–39 | 13.7% | 21.5% |
| 40–44 | 15.3% | 22.2% |
| 45–49 | 16.4% | 22.9% |
| 50–54 | 18.9% | 25.2% |
| 55–59 | 20.9% | 26.3% |
How these estimates are calculated
US Navy circumference method
Developed by Hodgdon and Beckett at the Naval Health Research Center in 1984 and calibrated against hydrostatic weighing on 1,022 Navy personnel. The metric equations are:
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) + 0.221·log₁₀(height)) − 450
The standard error of estimate is 3.52% for men and 3.72% for women. The method is known to under-read for very muscular builds and over-read slightly for very lean women, because circumference at a given site reflects both fat and the muscle underneath it.
Deurenberg BMI method
Published by Deurenberg, Weststrate and Seidell in the British Journal of Nutrition in 1991, fitted on 1,229 subjects aged 7 to 83:
Adults (over 15): %BF = 1.20·BMI + 0.23·age − 10.8·sex − 5.4
Children (15 and under): %BF = 1.51·BMI − 0.70·age − 3.6·sex + 1.4
where sex = 1 for males, 0 for femalesThe adult equation has R² = 0.79 and a standard error of 4.1%; the child equation is weaker (R² = 0.38, SEE 4.4%). It is included here as a sanity check, since it uses no tape measurements and therefore fails in the opposite direction to the Navy method. The authors note it slightly overestimates in obese subjects.
Fat mass and lean mass
Fat mass = weight × %BF / 100 Lean mass = weight − fat mass
"Fat to lose" holds lean mass constant rather than scaling weight down proportionally, which is why the target weight is lean mass / (1 − target%/100) and not a simple percentage of your current weight.
This is an estimate, not a diagnosis. Circumference and BMI equations are population regressions and can be several points off for any individual. For clinical decisions, use DEXA, air-displacement plethysmography, or hydrostatic weighing, and talk to a healthcare professional.
Medical disclaimer. This calculator is for general information and education only. It is not medical advice, not a diagnosis, and not a substitute for professional care. Tape-measure estimates carry a margin of several percentage points against DEXA or hydrostatic weighing, and are least reliable at very low and very high body fat.Speak to a doctor or another qualified clinician about any health decision.Last reviewed .
Frequently asked questions
How accurate is the US Navy body fat calculator?
The Navy circumference equations were validated against hydrostatic (underwater) weighing on 1,022 US Navy personnel by Hodgdon and Beckett in 1984. The standard error of estimate is 3.52% for men and 3.72% for women, which means roughly two thirds of results land within about 3.5 points of the hydrostatic value and the rest fall further out. Treat the number as a band, not a precise reading: an estimate of 18% is really "roughly 15% to 22%".
Why does the calculator ask women for a hip measurement but not men?
The Navy method uses two different regressions. The male equation is driven by waist minus neck; the female equation uses waist plus hip minus neck, because hip circumference carries most of the information about gynoid fat distribution. Substituting the waist for a missing hip measurement would shift a female result by several percentage points, so this calculator declines to estimate rather than return a number it knows is wrong.
Why do the Navy and BMI methods disagree?
They measure different things. The Navy method reads your actual body shape through tape measurements. The Deurenberg BMI equation is a population regression on height and weight alone, so it cannot tell muscle from fat — a heavily muscled person reads high, and someone with low muscle mass at a normal weight reads low. A large gap between the two is informative in itself: it usually means your build is further from the population average than BMI assumes.
Where do the body fat categories come from?
The Essential / Athletes / Fitness / Average / Obese bands are the American Council on Exercise (ACE) classifications. They differ by sex because women carry more essential fat — the minimum required for normal physiological function is about 2–5% for men and 10–13% for women. Below the essential threshold, hormonal and immune function are affected.
What is the difference between body fat percentage and BMI?
BMI is weight divided by height squared. It is a screening proxy that says nothing about composition: two people with identical BMI can have very different amounts of fat and muscle. Body fat percentage states directly what fraction of your weight is fat tissue, which is why it tracks health risk more closely than BMI for athletic, older, or very lean people.
How should I take the tape measurements?
Measure on bare skin with a flexible tape, keeping it level and snug without compressing the skin, and exhale normally rather than sucking in. Measure the neck just below the larynx, sloping slightly downward at the front. Measure the male waist at the navel, and the female waist at its narrowest point. Measure hips at the widest point of the buttocks. Repeat each measurement and take the average — a 1 cm error on the waist moves the result by roughly a full percentage point.
Is my data sent anywhere?
No. Every calculation runs in your browser. Nothing you type is uploaded, stored, or logged, and the page keeps working offline once loaded.