Body Fat Calculator
Estimate your body fat percentage from a few tape measurements using the U.S. Navy method — with your category, fat mass and lean body mass, in US or metric units.
Measure to the nearest quarter inch (0.5 cm). Waist at the navel for men and at the narrowest point for women; neck just below the larynx; hip at the widest point.
| Description | Women | Men |
|---|---|---|
| Essential fat | 10–13% | 2–5% |
| Athletes | 14–20% | 6–13% |
| Fitness | 21–24% | 14–17% |
| Average | 25–31% | 18–24% |
| Obese | 32%+ | 25%+ |
Ranges published by the American Council on Exercise. The row matching your result is highlighted. Falling below the essential range is not a fitness goal — that level of fat is needed for normal hormonal and organ function.
| Age | Women | Men |
|---|
These are the reference values the calculator interpolates between. They apply from age 20 to 55; outside that range no ideal figure is shown, because the underlying data does not cover it.
What body fat percentage actually tells you
Body fat percentage is the share of your total weight made up of fat tissue. Everything else — muscle, bone, organs, connective tissue, water — is lean body mass. Two people can weigh exactly the same and sit ten points apart on body fat, which is precisely why the number is more useful than the scale on its own.
Not all of that fat is spare. Essential fat is the amount needed for the body to work: it cushions organs, insulates, and is bound up in cell membranes and hormone production. It runs around 2–5% in men and 10–13% in women, and the gap is not a matter of fitness — women carry more essential fat for reproductive and hormonal reasons. Storage fat is what accumulates on top of that, some under the skin and some, more consequentially, packed around the abdominal organs as visceral fat.
That distinction matters more than the headline number. Visceral fat is metabolically active tissue that releases signalling proteins affecting insulin sensitivity and inflammation, and it tracks with waist size specifically. Subcutaneous fat on the hips and thighs carries far less of that risk. A tape measure around the waist is picking up the more informative kind almost by accident.
How this calculator works
The primary estimate uses the U.S. Navy circumference method, developed at the Naval Health Research Center in the 1980s. It predicts body fat from the ratio between your girth measurements and your height, on the basis that fat accumulates in predictable places. The equations are:
BFP = 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450
Women
BFP = 495 ÷ (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450
All measurements in centimetres. US entries are converted first.
Both unit tabs run through these same metric equations — inches and pounds are converted to centimetres and kilograms first. There is also an inch-based form of the Navy method in circulation, algebraically converted from this one, and it can land a few tenths of a point away because of rounding in the conversion. If a result here differs slightly from another calculator, that is usually why. Running one set of equations for both tabs is what keeps this page from contradicting itself when you switch between them.
Notice what the equations use and what they ignore. Weight appears nowhere in them — your body fat percentage comes purely from girth and height. Weight is used afterwards, to turn that percentage into pounds or kilograms:
Worked through with the values this page opens on — a 28-year-old man, 176 lb, 5′11″, 15″ neck, 34″ waist — the result is 17.0% body fat, which is 29.9 lb of fat mass against 146.1 lb of lean mass, landing in the fitness band.
The second estimate on the result card uses the BMI method, which infers body fat from height, weight and age instead of girth. For adults it is 1.20 × BMI + 0.23 × age, minus 16.2 for men or 5.4 for women; under 18 a separate pair of equations applies. It is shown as a cross-check, not as a competing answer — see the section below on why the two disagree.
The ideal body fat row draws on the Jackson & Pollock reference values, interpolating linearly between the published five-year steps. It covers ages 20 to 55; outside that range the row is hidden rather than extrapolated, because the source data does not support it.
Taking the measurements properly
The arithmetic is fixed; the measuring is where the error comes from. A one-inch mistake on the neck moves the result by around two percentage points, which is larger than most of the change you would see from a month of genuine effort. Getting it consistent matters more than getting it perfect.
- Neck — just below the larynx, with the tape sloping slightly downward toward the front. Keep your shoulders down and do not flare the neck outward.
- Waist — at the navel for men, at the narrowest point for women. Measure at the end of a normal breath out. Do not pull your stomach in; it is the single most common way people flatter their own result.
- Hips (women) — around the widest part of the buttocks, tape level all the way round.
- Height — without shoes, heels together, standing tall.
Body measurements come up outside fitness too. Our bra size calculator converts band and cup measurements between sizing systems, and the shoe size converter handles US, UK, EU and Japanese sizes.
Use a flexible tape, snug enough not to sag but not tight enough to compress the skin. Measure to the nearest quarter inch or half centimetre. Take each measurement in the morning before eating, and repeat each one twice — if the two readings disagree by more than a quarter inch, take a third.
What the ranges mean
The categories on this page come from the American Council on Exercise. For men: 2–5% essential, 6–13% athletes, 14–17% fitness, 18–24% average, 25% and above obese. For women each band sits roughly eight to ten points higher: 10–13% essential, 14–20% athletes, 21–24% fitness, 25–31% average, 32% and above obese.
Two cautions about reading those bands. The first is that "athletes" describes a body composition, not an achievement — sitting in that range without the training behind it is not the same thing. The second, and more important, is that lower is not uniformly better. Dropping to or below the essential range is associated with hormonal disruption, reduced bone density, impaired immune function and, in women, disrupted or absent menstruation. The bands describe a distribution, not a ladder to climb.
Why the two methods disagree
The result card shows two numbers, and they frequently differ by several points. That gap is informative rather than a fault.
The Navy method responds to your shape: it asks where your body carries girth, so a lean, broad-shouldered build and a soft, narrow one get different answers even at identical weights. The BMI method has no shape input at all — feed it the same height, weight and age and it returns the same figure whether the weight is muscle or fat. That is BMI's well-known weakness, and it does not disappear when BMI is converted into a body fat estimate.
So when the BMI figure comes out well above the Navy figure, it usually means you carry more muscle than the formula assumes. When it comes out well below, the reverse. With the default figures on this page the Navy method gives 17.0% and the BMI method 19.7% — a gap of under three points, which is unremarkable. A gap of eight or ten points is worth noticing, and generally says more about your build than about either calculation being wrong.
How accurate is the tape method?
Honestly: useful, not precise. Research on the circumference method generally places it within about three to four percentage points of a DEXA scan for most adults. Hydrostatic weighing, air displacement plethysmography and DEXA are all substantially more accurate, and all require equipment you do not have at home.
The error is not evenly spread. The method performs worst at the extremes — very lean people, very heavy people, and heavily muscled builds — because it is inferring fat from girth, and a thick waist from abdominal muscle reads the same to a tape as a thick waist from fat. It also cannot see where fat sits, so two people at the same percentage can carry very different visceral loads.
What it does well is repeat. Measured the same way, in the same conditions, week after week, the direction and size of change are meaningful even when the absolute number carries a few points of uncertainty. Treat a single reading as a rough position and a series of readings as the actual signal.
Changing your body fat
Body fat percentage is a ratio, so it moves when either part of it moves. Losing fat lowers it; gaining lean mass lowers it too, even at unchanged weight. That second route is why the scale can sit still for weeks while the number here falls.
Strength work is measured differently from cardio. Our one rep max calculator estimates your 1RM from any set, which is how most training percentages are prescribed.
The practical implication is that fat loss and muscle retention are one problem, not two. A large calorie deficit strips lean mass alongside fat, which lowers the weight without improving the ratio much; a moderate deficit combined with resistance training and adequate protein preserves far more of it. This is also why the calculator reports lean body mass as its own row — watching that figure hold while fat mass falls tells you the deficit is the right size, and watching it drop tells you it is not.
Expect slow movement. A percentage point a month is a realistic pace for most people, and it is small enough to be buried under measurement noise from a single reading, which is the case for measuring consistently rather than often.
What this calculator does not cover
Being clear about the edges matters more than the estimate looking authoritative.
- Where the fat is. Visceral fat around the organs carries far more health risk than subcutaneous fat, and a single percentage cannot separate them.
- Pregnancy. The equations assume a non-pregnant body; the measurements are not meaningful during pregnancy.
- Children. The Navy equations were developed on adults. The BMI method here switches to youth equations under 18, but body composition in growing bodies is properly assessed against age- and sex-specific growth charts by a clinician.
- Unusual builds. Competitive strength athletes, people with significant muscle loss, amputees and anyone with fluid retention will all get distorted results.
- Medical conditions. Oedema, thyroid disorders and some medications change body composition and water balance in ways this cannot account for.
If your result concerns you, or you are making decisions about your health from it, take it to a doctor or a registered dietitian rather than acting on it alone. If you want the related figures, the BMI calculator, lean body mass calculator and ideal weight calculator approach the same question from different angles.
Frequently asked questions
How accurate is the U.S. Navy body fat calculator?
Studies of the circumference method generally put it within about 3 to 4 percentage points of a DEXA scan for most people, which is close enough to track a trend but not to treat as a precise figure. It is least reliable at the extremes — very lean, very heavy, or heavily muscled builds — because it infers fat from girth rather than measuring it. Its real strength is repeatability: measured the same way each time, the direction of change is meaningful even when the absolute number is not.
What is a healthy body fat percentage?
By the American Council on Exercise ranges, men sit in the fitness band from 14% to 17% and the average band from 18% to 24%, with 25% and above classed as obese. For women the same bands are 21% to 24% and 25% to 31%, with 32% and above classed as obese. Women carry more essential fat than men for reproductive and hormonal reasons, which is why every band sits roughly 8 to 10 points higher.
How do I measure my neck and waist correctly?
Use a flexible tape, keep it snug without compressing the skin, and measure to the nearest quarter inch or half centimetre. Neck goes just below the larynx with the tape sloping slightly downward at the front. Waist goes at the navel for men and at the narrowest point for women. Women also measure the hips at their widest point. Measure at the same time of day, ideally in the morning before eating, and do not pull your stomach in.
Why does the calculator ask for my hip measurement only if I am female?
The Navy equation for women includes hip circumference and the one for men does not. Female fat distribution is weighted more toward the hips and thighs, so waist alone predicts it poorly. The hip row appears when you select female and is hidden otherwise, because the male equation has no term to put it in.
Why do the Navy method and the BMI method give different numbers?
They measure different things. The Navy method estimates fat from where your body actually carries girth, so it responds to your shape. The BMI method infers it from height, weight and age only, so two people with the same BMI get the same answer regardless of build. The BMI figure is shown as a cross-check: a large gap between the two usually means you are more muscular or more lightly built than the BMI formula assumes.
What is lean body mass?
Everything that is not fat — muscle, bone, organs, connective tissue and water. It is your total weight minus your fat mass. It is worth tracking alongside body fat, because losing weight while lean mass falls is a different outcome from losing weight while it holds steady, even when the scale moves identically.
Can body fat be too low?
Yes. Essential fat is roughly 2 to 5% for men and 10 to 13% for women, and it is needed for hormone production, temperature regulation and organ protection. Sustained levels at or below that range are associated with hormonal disruption, loss of bone density, poor immune function and, in women, disrupted or absent menstruation. Very low body fat is not a fitness goal and is worth discussing with a doctor rather than chasing.
What does the ideal body fat figure mean?
It comes from the Jackson & Pollock reference values, which describe the body fat percentage typically associated with good health at a given age, rising gradually as you get older. The calculator interpolates between the published ages, and shows nothing outside 20 to 55 because the underlying data does not cover those ages. Treat it as a reference point rather than a target handed down for you personally.
This calculator provides an estimate for general information and educational purposes only. It is not medical advice, a diagnosis, or a substitute for professional care, and the U.S. Navy circumference method is an approximation that can differ meaningfully from a clinical body composition measurement. Do not use it to diagnose or treat any condition. If you have concerns about your weight, body composition or eating patterns, speak with a doctor or registered dietitian. Learn more about how we build these tools or read our privacy policy.