Free body fat % calculator
Find your body fat percentage in two seconds. Pick male or female, enter your height, neck, and waist (women add hips), and the calculator returns your body fat percentage using the US Navy circumference method, plus the ACE category it falls in — updated live, as you type.
On this page15 sections
Circumference methods have an error range of ±3–4%. For clinical accuracy, use DEXA or hydrostatic weighing.
Results are estimates. Consult a professional.
What is body fat percentage?
Body fat percentage is the share of your total body weight that is fat, as opposed to muscle, bone, organs, and water. It is the single most direct read on body composition — far more telling than weight or BMI alone, because two people of identical height and weight can carry wildly different amounts of fat. This body fat calculator estimates that percentage from a few simple tape measurements using the US Navy circumference method, the moment you enter your height and girths in centimetres.
Where the scale tells you how heavy you are and BMI tells you weight relative to height, body fat percentage tells you what your weight is made of. A lean, muscular athlete and a sedentary person can weigh the same; their body fat percentages will not. That is why coaches, the military, and clinicians track body fat alongside weight — it is the number that separates muscle from fat.
How to measure for the body fat calculator
The Navy method is only as accurate as your tape work. A centimetre or two in the wrong place can move the result by a couple of percentage points, so measure carefully with a soft cloth tape, on bare skin, and at the end of a normal breath — never sucking in or pushing out.
- Height. Stand straight against a wall without shoes and record your height in centimetres.
- Neck. Wrap the tape around your neck just below the Adam's apple, sloping slightly down at the front. Keep it snug, not tight.
- Waist (men). Measure horizontally around the navel, relaxed, at the end of a normal exhale. Don't pull the tape into your skin.
- Waist (women). Measure around the narrowest part of the torso, usually just above the navel.
- Hip (women only). Measure around the fullest part of the hips and seat, feet together.
A worked example using the body fat calculator
Tom is 180 cm tall, with a 84 cm waist and a 38 cm neck. He selects male and enters the three measurements. Here is exactly the arithmetic the calculator runs — the men's Navy formula on centimetre inputs.
Step 1 — Subtract neck from waist
The formula works off the gap between the waist and the neck: 84 − 38 = 46 cm. A bigger gap means more fat stored at the waist relative to the frame.
Step 2 — Take the two logarithms
The Navy formula uses base-10 logs: log10(46) ≈ 1.6628 and log10(180) ≈ 2.2553. These are what let circumference scale with height.
Step 3 — Plug into the men's formula
Now see how that compares. A man in the ACE 'fitness' range carries 14–17% body fat, and athletes 6–13%. To move from 21.8% toward the fitness band, Tom would need to lose fat while holding onto muscle — the next sections cover the category chart and how to get there.
Body fat percentage chart by sex (ACE categories)
Once you have a number, the question is what it means. The most widely used reference is the American Council on Exercise (ACE) five-category chart. Women's healthy ranges sit higher than men's at every level — about 8–10 percentage points — because women carry more essential fat for reproductive and hormonal function. That difference is biology, not a worse result.
| Category | Women | Men |
|---|---|---|
| Essential fat | 10–13% | 2–5% |
| Athletes | 14–20% | 6–13% |
| Fitness | 21–24% | 14–17% |
| Acceptable (average) | 25–31% | 18–24% |
| Obese | 32%+ | 25%+ |
Source: American Council on Exercise (ACE) general body-fat categories. ACSM uses very similar bands.
Healthy body fat ranges by age and sex
A single chart cannot capture everyone, because healthy body fat drifts upward with age. As people get older they tend to lose muscle and gain fat, so the same percentage that signals concern at 25 can be perfectly normal at 55. The age-banded ranges below, based on Jackson & Pollock norms, are a more forgiving guide than the single ACE bands.
| Age | Women (healthy) | Men (healthy) |
|---|---|---|
| 20–39 | 21–32% | 8–19% |
| 40–59 | 23–33% | 11–21% |
| 60–79 | 24–35% | 13–24% |
Healthy-range guide by age, after Jackson & Pollock / WHO-aligned norms. Below these ranges is 'lean'; above is 'high'.
The takeaway: judge your number against your age and sex, not a single universal target. A 55-year-old woman at 30% is in a healthy range; a 25-year-old man at 30% is carrying high body fat. Use the band that matches you.
Navy method vs DEXA, calipers, and BIA
The Navy circumference method is one of several ways to estimate body fat, each trading accuracy for cost and convenience. No tape-measure method matches a lab scan, but the Navy formula is remarkably good for something that needs nothing but a tape measure. Here is how the common methods stack up.
| Method | How it works | Typical accuracy | Cost / access |
|---|---|---|---|
| DEXA scan | X-ray of fat, muscle, and bone | ±1–2% (gold standard) | Clinic, ~$50–150 |
| Hydrostatic weighing | Underwater body density | ±2% | Specialist lab |
| Skinfold calipers | Pinch thickness at sites | ±3–4% (skilled tester) | Cheap, needs skill |
| US Navy (this tool) | Tape circumferences | ±3–4% of DEXA | Free, tape only |
| BIA scales / handhelds | Electrical impedance | ±4–8%, hydration-sensitive | Cheap, very convenient |
Approximate, typical accuracy versus DEXA. Validation studies put the Navy method within about 3–4% of DEXA for most people.
In practice the Navy method is more reliable than the bioelectrical-impedance (BIA) readout on a bathroom scale, which swings with hydration, and competitive with skinfold calipers in untrained hands. DEXA remains the reference, but for a free estimate you can repeat at home, the Navy method is hard to beat.
How to lower your body fat percentage
Body fat percentage falls when you lose fat while keeping muscle — not simply when you lose weight, which can shed muscle and barely move the percentage. There is no way to spot-reduce a single area; fat comes off your whole body in your own genetic pattern. The levers that actually work are unglamorous and consistent.
- Run a modest calorie deficit. Eat roughly 250–500 calories below your maintenance level. A slow, steady deficit preserves muscle far better than a crash diet.
- Lift weights. Resistance training tells your body to keep muscle while you lose fat, so the percentage drops even if the scale moves slowly.
- Eat enough protein. Around 1.6–2.2 g per kg of body weight protects muscle in a deficit and keeps you full.
- Be patient and consistent. A sustainable rate is about 0.5–1% of body fat per month; track the trend monthly, not daily.
Pair this calculator with the tools that handle the energy side: a calorie deficit calculator to size your target, and the FFMI calculator to track the muscle you are protecting as the fat comes off.
How accurate is this body fat calculator?
For most people the Navy method lands within about 3–4% of a DEXA scan — close enough to place you in the right category and, more importantly, to track your own change reliably over time. Where it slips is at the extremes and for unusual body types.
Where it is least reliable
- Very lean or very heavy people. The formula was built around mid-range body fat and drifts at the ends.
- Muscular necks. A thick, trained neck shrinks the waist−neck gap and can make the tool underestimate body fat.
- Non-standard fat distribution. The Navy formula assumes a typical pattern; bodies that store fat differently read less accurately.
Body fat definitions
Sources and methodology
This calculator uses the US Navy circumference method, developed at the Naval Health Research Center, with measurements in centimetres. Category bands come from the American Council on Exercise (ACE) general body-fat chart, with age-banded healthy ranges after Jackson & Pollock norms. Accuracy figures reflect published validation of the Navy method against DEXA, the reference standard.
American Council on Exercise (ACE) — general body-fat percentage categories.Hodgdon JA, Beckett MB. "Prediction of percent body fat for U.S. Navy men and women from body circumferences and height." Naval Health Research Center, 1984.Frequently asked questions about the free body fat % calculator
About this body fat calculator
This body fat calculator runs entirely in your browser. Your height, neck, waist, and hip measurements never leave your device — nothing is sent to a server, logged, or shared. It applies the US Navy circumference formula to your measurements and matches the result to standard body-fat categories, updating instantly on every change.
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