Free body-composition calculator
Body Fat Calculator
Estimate your body-fat percentage three ways — the U.S. Navy tape method, skinfold calipers, or a quick height-and-weight estimate. See your lean mass, fat mass, and FFMI, then carry the number straight into our lean-mass and recomp tools.
Pick the method you can actually measure. Sample numbers are filled in — change any field to see your own body fat.
U.S. Navy method — just a tape measure. The most popular at-home method.
The published formulas use sex-specific coefficients. Not a gender identity field.
Used to turn your body-fat % into fat mass and lean mass.
The Navy formula uses your height alongside the tape measurements.
Measure just below the Adam's apple, tape level.
Measure around your belly at the navel, after a relaxed breath out.
Edit any field above to see your body-fat %, category, lean and fat mass, and a Strength Score bridge.
Free. No signup. Works on your phone in the gym.
These are field-formula estimates, not a medical test. They carry an error of a few percentage points. This is a fitness utility — don't use it for clinical decisions, eating-disorder recovery, pregnancy, or under-18 body composition.
How each method works
There's no way to measure body fat directly without a lab. Every at-home method estimates it from something you can measure — circumferences, skinfold thickness, or just height and weight. This calculator gives you the three most useful options and lets you pick whichever you can actually do.
Tape method (U.S. Navy)
The most popular no-equipment method. You measure a few circumferences with a tape measure — neck and belly for men; neck, waist, and hips for women — plus your height. Those go into the Hodgdon-Beckett equations the U.S. military uses for body-composition screening. It's fast and needs nothing but a tape, but it loses accuracy for very lean, very muscular, or very heavy people, because it's really measuring shape, not fat directly.
Skinfold calipers (Jackson-Pollock)
The most accurate at-home option when done well. You pinch a fold of skin and underlying fat at specific sites and measure its thickness in millimetres. The Jackson-Pollock equations turn the sum of those folds — plus your age — into body density, and then a conversion (Siri by default, Brozek as an alternative) turns density into a body-fat percentage. The 3-site version is quick; the 7-site version averages more locations and is a bit more robust. The catch: results swing with technique, so measure the same way every time.
Height & weight estimate (BMI-based)
The fallback for when you have no tape and no caliper. It uses the Deurenberg equation, which estimates body fat from your BMI, age, and sex. Because BMI can't tell muscle from fat, this is the least accurate method — a lean, muscular lifter and a sedentary person with the same height and weight get the same estimate. Use it for a rough ballpark, then upgrade to a tape or caliper when you can.
The formulas in this calculator
- U.S. Navy (circumference)
Men:
86.010 × log₁₀(belly − neck) − 70.041 × log₁₀(height) + 36.76Women use waist + hip − neck with their own coefficients. All measurements are in inches in the original; for metric we convert your centimetres to inches first so the result matches the official equation exactly. We use the direct Navy formula, not the "metric density" variant that some calculators publish — they don't give identical numbers.
- Jackson-Pollock (skinfold)
- The 3-site and 7-site equations estimate body density from the sum of your skinfolds and your age. Men and women have separate coefficients, and the 3-site sites differ by sex (men: chest, abdomen, thigh; women: triceps, suprailiac, thigh). We then convert density to body-fat % with the Siri equation —
BF% = 495 ÷ density − 450— and show the Brozek alternative alongside. - Deurenberg (BMI-based)
BF% = 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4(sex = 1 for men, 0 for women). A reasonable population-level estimate with a standard error around 4 percentage points — but blind to how muscular you are. Adults only.
Body-fat percentage ranges
These are the American Council on Exercise categories — a common fitness convention, not a medical diagnosis. Women carry more essential fat than men for normal physiology, so the ranges differ by sex.
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletic | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Above average | 25%+ | 32%+ |
A floor, not a target. Essential fat is the minimum your body needs to function. Dropping toward it — below about 6% for men or 14% for women — can disrupt hormones, recovery, and (for women) menstrual cycles. Lower is not automatically better.
How accurate is each method?
Every at-home method is an estimate. Here's roughly how they stack up — and why consistency matters more than picking the "best" one.
| Method | Confidence | Notes |
|---|---|---|
| DEXA scan | High | Lab reference standard. Still affected by hydration; not an at-home option. |
| Skinfold calipers | Medium–high | Trained tester, consistent sites: good for serial tracking. Untrained: error climbs fast. |
| Navy / tape method | Medium | Standard error around 3.5 points. Best near average builds; weaker at the extremes. |
| BMI estimate | Low | Can't tell muscle from fat. Standard error around 4 points; worst for muscular lifters. |
| Visual estimate | Low | Wide error bars even for trained eyes. A sanity check, not a tracking input. |
Consistency beats precision. The same method, measured the same way every couple of weeks, gives a better trend than jumping between methods. Don't compare a skinfold reading to a tape reading — they're different estimates of the same thing.
Common body-fat measurement mistakes
- Treating one reading as exact. Every method carries a few percentage points of error. The trend over weeks is the signal; a single decimal is noise.
- Switching methods. A 15% tape reading and a 15% caliper reading aren't the same measurement. Pick one and stick with it.
- Measuring under different conditions. Hydration, a recent meal, a pump from training, or a sweaty pinch site all move the number. Same time of day, same conditions.
- Using the tape method on a very muscular or very lean build. The Navy equation assumes an average shape. At the extremes it drifts — usually overestimating very lean lifters and underestimating heavier ones.
- Chasing essential-fat numbers. Very low body fat isn't a goal in itself. Below the essential-fat floor, health and performance suffer.
Methodology
The tape method uses the official U.S. Navy (Hodgdon-Beckett) circumference equations, evaluating them as continuous formulas without the military worksheet's intermediate rounding. Metric inputs are converted to inches first so the result matches the canonical inch equation. The skinfold method uses the Jackson-Pollock (men) and Jackson-Pollock-Ward (women) body-density equations, converted to body-fat % with Siri by default and Brozek as an alternative. The no-tools estimate uses the adult Deurenberg equation.
Lean and fat mass come straight from your result: fat mass = weight × body-fat % ÷ 100, and lean mass is the remainder. FFMI is lean mass ÷ height². The Strength Score bridge reuses Stronger's strength standards to place a lift on the Beginner → World Class scale.
These are estimates with real error bands. They drift for very muscular athletes, contest-lean physiques, people with obesity, older adults, pregnancy and postpartum, and anyone measuring inconsistently. This is a fitness utility — for clinical decisions, eating-disorder recovery, pregnancy, or under-18 body composition, use clinician-guided measurement.
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Open Barbell CalculatorFrequently asked questions
How accurate is a body fat calculator?
These are field-formula estimates, not lab measurements. The Navy tape method has a standard error of roughly 3.5 percentage points; skinfold calipers can be tighter in trained hands but vary a lot with technique; the BMI-based estimate is the loosest because it can't tell muscle from fat. Track the trend with one method instead of chasing decimals.
Which method should I use?
If you own a caliper and can measure carefully, the skinfold method is the most accurate at-home option. If not, the Navy tape method is the best no-equipment choice — all you need is a tape measure. The height-and-weight estimate is a last resort; it's the least accurate, especially for muscular lifters.
How do skinfold calipers work?
You pinch a fold of skin and fat at specific sites and measure its thickness in millimetres. The Jackson-Pollock equations turn the sum of those folds (plus age) into body density, then a conversion like Siri turns density into a body-fat %. The 3-site version is quicker; 7-site is more thorough. Accuracy depends heavily on consistent technique.
What's the difference between Siri and Brozek?
Both convert body density into a body-fat %. Siri is the common default; Brozek is an alternative that lands within a few tenths of a percent. The calculator uses Siri by default and shows Brozek alongside so you can see the small difference.
What's a healthy body-fat percentage?
Using the American Council on Exercise categories: for men, 2–5% is essential, 6–13% athletic, 14–17% fitness, 18–24% average, 25%+ above average. For women, 10–13% essential, 14–20% athletic, 21–24% fitness, 25–31% average, 32%+ above average. Women carry more essential fat for normal physiology. These are fitness conventions, not diagnoses.
Can body fat be too low?
Yes. Below roughly 6% for men and 14% for women, you're at or below essential-fat levels, which can carry real health risks — hormonal disruption, lost cycles, poor recovery. A very low number is not a trophy. If you're cutting hard or noticing symptoms, ease off and, if needed, talk to a clinician.
Can I use this body-fat number in your other calculators?
Yes — that's what the handoff buttons under your result do. Your body-fat estimate (plus weight, height, age, sex) carry straight into the Lean Body Mass Calculator or the Body Recomp Calculator. No re-entering anything.
Is this calculator a medical device?
No. This is a fitness education and training tool — not a medical device. Don't use it for diagnosis, eating-disorder recovery, pregnancy decisions, pediatric assessment, or anything that should be clinician-guided. The estimates here are for adults.
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The calculator gives you the number. Stronger logs every set, scores your strength on the major lifts, and shows whether you're actually getting stronger.
