Body Fat Calculator

Estimate your body fat percentage with three validated methods: U.S. Navy tape measure, Jackson-Pollock 3-site skinfold, and the BMI-based Deurenberg formula. Get your fat mass, lean body mass and ACE fitness classification — metric or imperial — instantly, free, no signup.

Measure neck, waist (and hips for women) with a tape. Most accurate of the no-tool methods.
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kg
cm
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Body Fat (U.S. Navy)
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Fat mass — Estimated mass of body fat
Lean body mass — Muscle, bone, organs, water
Where You Fall on the ACE Scale
Body fat percentage ACE classification scale
Compare with Other Methods
Method Body Fat % Category

What Is Body Fat Percentage?

Body fat percentage (BF%) is the proportion of your total body mass that is made up of fat tissue. Unlike BMI, which only uses weight and height, body fat percentage distinguishes fat from lean mass — muscle, bone, organs and water. This makes it a far better indicator of body composition, fitness level and metabolic health. A muscular athlete and a sedentary office worker can share the same BMI while differing dramatically in body fat percentage, with very different health implications.

Body fat comes in two forms: essential fat, which is required for hormone production, vitamin absorption, temperature regulation and organ protection, and storage fat, which accumulates beyond essential needs. Essential fat sits at roughly 2–5% for men and 10–13% for women — the higher female threshold reflects sex-specific tissue around breasts, hips and the reproductive system.

How This Body Fat Calculator Works

This calculator offers three independent methods, each backed by published research. You can pick the one that matches the equipment you have on hand, and compare the three side-by-side in the results panel.

1. U.S. Navy Circumference Method

Developed by the U.S. Naval Health Research Center in the 1980s and used for military fitness assessments, this method needs only a soft measuring tape. The formula relies on neck, waist and — for women — hip circumferences combined with height. Typical accuracy is within ±3–4% body fat when measurements are taken correctly.

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

All measurements in centimeters. Tip: measure the waist at navel level and the neck just below the larynx, breathing out lightly. Pull the tape snug but never tight enough to compress the skin.

2. Jackson-Pollock 3-Site Skinfold Method

Developed by exercise physiologists Andrew Jackson and Michael Pollock in the late 1970s, this method requires skinfold calipers (Accu-Measure, Slim Guide or Harpenden). It is considered one of the most reliable field methods and is widely used in sports science. Accuracy is typically ±3% body fat when sites are pinched consistently.

The three sites differ by sex:

The calculator applies the Jackson-Pollock body-density equation, then converts to body fat percentage using the Siri equation: BF% = (495 / density) − 450.

3. BMI-Based (Deurenberg Equation)

When you have no tape and no calipers, the Deurenberg equation derives a rough body fat percentage from BMI, age and sex. It is the least accurate of the three (typically ±5–8% body fat) because it inherits BMI's main flaw — it cannot tell muscle from fat — but it is useful as a quick sanity check.

Formula: BF% = 1.20·BMI + 0.23·age − 10.8·sex − 5.4 (where sex = 1 for men, 0 for women)

ACE Body Fat Classification

The American Council on Exercise (ACE) publishes sex-specific body fat thresholds widely used by trainers, dietitians and gyms. They are not diagnostic categories — they describe fitness levels rather than disease risk — but they give a clear reference point for any healthy adult.

Men:

Women:

Fat Mass and Lean Body Mass

The calculator also breaks your total weight into two components:

Tracking lean body mass over time is far more meaningful than tracking weight alone. A successful body recomposition program reduces fat mass while preserving or increasing lean mass, which on a scale may appear as little or no weight change despite real progress.

Accuracy and Limitations

No field method matches the gold standards — DEXA scans, hydrostatic weighing or air-displacement plethysmography (Bod Pod) — which can cost USD 50–200 per session. Field methods are estimates, and even DEXA varies by ±1–2% between machines. The most useful approach is to pick one method, take measurements under the same conditions (time of day, hydration, fasted state) and track the trend over weeks rather than chasing a single absolute number.

These calculators are not suitable for: pregnant women, people under 14, individuals with edema or fluid retention, very lean athletes whose body fat falls below the validation range, or anyone with extreme limb-to-trunk ratios. Always discuss significant body composition changes with a doctor or registered dietitian if you have underlying health conditions.

Body Fat Calculation Examples

Man, 30 yrs, 175 cm, 75 kg — U.S. Navy (neck 38 cm, waist 86 cm)
BF% = 495 / (1.0324 − 0.19077·log10(86 − 38) + 0.15456·log10(175)) − 450
    = 495 / (1.0324 − 0.19077·1.6812 + 0.15456·2.2430) − 450
    = 495 / 1.0584 − 450
    ≈ 17.7%   →  Fitness (ACE, men 14–18%)
Fat mass  = 75 × 0.177 = 13.3 kg
Lean mass = 75 − 13.3 = 61.7 kg
Woman, 28 yrs, 165 cm — Jackson-Pollock 3-site (triceps 16, suprailiac 14, thigh 22 mm)
Sum = 52 mm
Density = 1.0994921 − 0.0009929·52 + 0.0000023·52² − 0.0001392·28
       ≈ 1.0502
BF% = (495 / 1.0502) − 450 ≈ 21.4%   →  Fitness (ACE, women 21–25%)
Man, 45 yrs, 180 cm, 95 kg — BMI-based (Deurenberg)
BMI = 95 / (1.80)² = 29.3
BF% = 1.20 × 29.3 + 0.23 × 45 − 10.8 × 1 − 5.4
    = 35.18 + 10.35 − 10.8 − 5.4
    ≈ 29.3%   →  Obese (ACE, men ≥ 25%)

Three methods, three answers — which one should you trust?

Editor’s note — by Amine H., last reviewed 27 May 2026.

A DEXA scan costs $50–200 and gives roughly ±2% accuracy. The three free methods on this page give ±3–5% in their training populations and considerably worse outside them. Pick the wrong method for your body type and the gap widens to 8–12%. Here is how to choose, and how to read the result the calculator just gave you.

U.S. Navy circumference method

Inputs: height, neck, waist (and hip circumference for women). Trained against hydrostatic weighing on U.S. Navy personnel in the 1980s (Hodgdon & Beckett, 1984). Best for: average-fitness adults with typical proportions. Worst for: very lean athletes (under-estimates body fat), heavy non-obese individuals with broad frames (over-estimates). Not valid during pregnancy. Accuracy: ±3–4% versus DEXA in the training population.

Jackson–Pollock 3-site skinfold

Inputs: caliper measurements at three sites (men: chest, abdomen, thigh; women: triceps, suprailiac, thigh). Requires a caliper (around $20) and ideally a second person to take the measurements consistently. Best for: anyone with caliper access. The most accurate of the three methods at population extremes (very lean and very heavy). Worst for: anyone trying to measure their own thigh skinfold solo — just don’t. Accuracy: ±3–4% with good measurement technique, ±8–10% without it.

Deurenberg BMI-based formula

Inputs: BMI, age, sex. The formula is Body Fat % = 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4 (sex = 1 for men, 0 for women). Convenient (no calipers, no tape measure) but inherits BMI’s blindness to body composition: a recreational lifter and a sedentary office worker with identical BMI get identical Deurenberg numbers. Accuracy: ±5% in average populations, ±10%+ in athletes. Use only when measurement is impossible.

How to pick

Average adult, no caliper, want a quick estimate → U.S. Navy. Trained, regularly lifts, has caliper access → Jackson–Pollock. No measurements available at all, just BMI → Deurenberg as a rough placeholder. Want clinical-grade precision → pay for a DEXA scan; nothing on this page replaces it.

Convergence is the real signal

Run all three methods on the same person. If Navy says 18%, Jackson–Pollock says 19%, Deurenberg says 17%, you’re between 17–19% — the agreement is the signal that you fit the average population each method was trained on. If they spread 15–25%, take it as a warning sign that at least one of them is poorly calibrated for your body composition.

Takeaway: Pick the method that matches your inputs and body type, not the one that gives the prettiest number. U.S. Navy for average adults, Jackson–Pollock for trained populations with caliper access, Deurenberg as a fallback only. Re-measure every 4–6 weeks under similar conditions (morning, hydrated, before breakfast) for a comparable trend — a single measurement is a snapshot, not a verdict.

Sources: ACE Fitness body-composition classification · Overview of body-fat measurement methods.

Frequently Asked Questions

If you have a quality caliper and someone trained to pinch consistently, the Jackson-Pollock 3-site skinfold method is generally the most accurate field option (±3% body fat). If you only have a tape measure, the U.S. Navy method is close behind (±3–4%). The BMI-based Deurenberg equation is the least accurate (±5–8%) and is best used as a quick estimate when no other measurements are available.

According to the American Council on Exercise (ACE), a healthy body fat percentage for men sits in the fitness range of 14–17% or the acceptable range of 18–24%. For women, the equivalent is 21–24% (fitness) or 25–31% (acceptable). Below the essential fat floor (2% men, 10% women) is dangerous and below the athlete range (6% men, 14% women) is rarely sustainable outside of competition.

BMI uses only weight and height and cannot distinguish fat from muscle, bone or water. Body fat percentage directly estimates how much of your weight is fat tissue versus lean tissue. A muscular athlete may have a BMI in the overweight range despite very low body fat, while a sedentary person can have a normal BMI but high body fat (a phenomenon called "skinny fat" or normal-weight obesity).

Use a soft, flexible measuring tape. For the neck, measure just below the larynx (Adam's apple) with the tape kept horizontal — do not tilt. For the waist, measure at the level of the navel, breathing out lightly, with the tape parallel to the floor. For the hips (women only), measure at the widest point of the buttocks. Keep the tape snug but never compressing the skin, and take each measurement twice — use the average.

Use the U.S. Navy method — it only requires a soft tape measure, which is far cheaper than calipers (or you can use a piece of string and a ruler in a pinch). The Navy method is nearly as accurate as skinfold measurements when taken carefully. The BMI-based method is the fallback option when you have nothing but a scale and a height measurement.

Once every 2–4 weeks is plenty. Body fat does not change overnight — short-term fluctuations are mostly water and stomach contents, not actual fat. Always measure at the same time of day, ideally first thing in the morning before eating or drinking, in the same hydration state. The trend over months matters far more than any single number.

No. The U.S. Navy, Jackson-Pollock and Deurenberg equations were all validated on non-pregnant adults aged roughly 18 and over. Children and adolescents have different body composition that changes rapidly with growth, and pregnancy alters water balance and fat distribution in ways these formulas cannot account for. Use age- and condition-appropriate medical references instead.

Yes. This tool runs entirely in your browser — your measurements are never sent to any server. Your values are saved locally on your device using localStorage so you can come back and refine your inputs later. No signup, no tracking, no data collection.

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