Health
Body Fat Calculator
Estimate your body fat percentage from a few tape measurements with the U.S. Navy method — neck, waist, and (for women) hip. See your body-fat category, lean body mass, and fat mass, in metric or imperial, updating as you type.
Your measurements
Tape measurements, taken snug on bare skin. The U.S. Navy method does the rest.
Sex
Height
Neckbelow the larynx
Waistat the navel
Weightoptional — for lean & fat mass
20.1%body fat
AverageAdd your weight to see lean body mass and fat mass.
No sign-up · Free
The basics
What body fat percentage tells you
Body fat percentage is the share of your total weight that is fat, rather than muscle, bone, organs, and water. It's the number that actually describes your composition — and unlike BMI, it can tell a lean, muscular frame apart from one carrying excess fat. The U.S. Navy method estimates it from a few tape measurements, no scale or lab needed.
fat ÷ total weight
It measures composition, not size
Two people at the same weight can have very different fat fractions. Body fat percentage splits that weight into the part that's fat and the part that isn't.
80 kg at 20% → 16 kg fat, 64 kg lean
circumferences → estimate
The Navy method needs only a tape
The formula reads body fat off the difference between your waist and neck (and hip for women), scaled by height. Cheap, repeatable, and good enough to track change.
neck, waist, height — plus hip for women
Method
How the Navy method works
Three steps: take the measurements, plug them into the sex-specific equation, and read off the category.
- 1
Measure neck, waist, and hip
Take the neck below the larynx and the waist on bare skin. Women also measure the hip at its widest point. Average two readings for each site.
neck · waist · (hip for women) - 2
Plug into the Navy equation
The formula divides a constant by a denominator built from the log of your circumference term and the log of your height — different coefficients for men and women.
495 ÷ (… − 0.19077·log₁₀(W−N) + 0.15456·log₁₀(H)) − 450 - 3
Read the category
Map the resulting percentage onto the ACE bands — essential, athletes, fitness, average, or obese — using the sex-specific thresholds.
men 18% → average · women 24% → fitness
Tape technique
How to measure correctly
The formula is only as good as the tape. Measure on bare skin, keep the tape level and snug (not biting in), and take each reading on a normal breath out. Where you place the tape matters more than anything else.
Neck
Where: Just below the larynx (Adam's apple), with the tape sloping slightly down to the front.
Tip: Look straight ahead and don't flare the tape out onto the shoulders — keep it snug at the narrowest point.
Waist
Where: For men, around the navel. For women, at the narrowest point of the natural waist.
Tip: Measure on bare skin at the end of a normal breath out — don't suck in or push the belly out.
Hip (women only)
Where: Around the widest part of the buttocks, with feet together.
Tip: Keep the tape level all the way round and parallel to the floor — a tilted tape reads long.
Reference
Body fat categories by sex
The ACE (American Council on Exercise) bands. Women's healthy ranges sit several points higher than men's because women carry more essential fat. Switch sex to see each set — these are the bands the calculator and chart use to color every result.
Essential fat2 – 5.9%
Athletes6 – 13.9%
Fitness14 – 17.9%
Average18 – 24.9%
Obese25% and above
Worked examples
See it for a man and a woman
The same method, run through the two equations. Each figure is computed live from the formula — switch tabs to compare.
Given height 178 cm (70″), neck 39 cm, waist 91 cm, weight 80 kg
Circumference term: 91 − 39 = 52
Navy equation → 20.1% body fat
Lean mass: 63.9 kg · Fat mass: 16.1 kg
Body fat = 20.1%Average
Quick chart
Body fat by waist size
How body fat climbs with waist circumference, holding a typical height and neck fixed. Find the waist closest to yours and read the estimate straight off — color-coded by category.
Body fat % by waist, holding height 178 cm and neck 39 cm fixed.
| Waist | Body fat | Category |
|---|---|---|
| 76 cm (30″) | 7.9% | Athletes |
| 81 cm (32″) | 12.4% | Athletes |
| 86 cm (34″) | 16.4% | Fitness |
| 91 cm (36″) | 20.1% | Average |
| 97 cm (38″) | 24.2% | Average |
| 102 cm (40″) | 27.4% | Obese |
| 107 cm (42″) | 30.3% | Obese |
| 112 cm (44″) | 33% | Obese |
Essential fatAthletesFitnessAverageObese
Worth knowing
What the estimate can and can't do
A tape-measure formula is a useful estimate, not a lab result. Knowing its limits keeps you from over-reading a single number.
estimate, not a scan
It's not DEXA or calipers
The Navy method predicts fat from circumferences. A DEXA scan, hydrostatic weighing, or skinfold calipers measure more directly and will usually disagree by a few points.
≈ ±3–4% vs a DEXA scan
a centimeter moves it
Measurement error compounds
Because the formula leans on the waist, small tape differences swing the result. Measure the same way each time and average two readings to keep change meaningful.
±1 cm at the waist → ≈ ±1% fat
floors differ by sex
Essential fat sets a floor
There is a minimum the body needs to function. Women's floor is higher than men's, which is why the whole female scale is shifted up.
men ≈ 2–5% · women ≈ 10–13%
water shifts size
Hydration and timing skew it
Bloating, a big meal, or a salty day change waist size and therefore the reading. Measuring at a consistent time — say, first thing in the morning — removes most of the noise.
measure on a normal exhale
Where it shows up
Why people track body fat
The percentage is a goal, a checkpoint, and a planning input all at once.
trend over time
Fitness tracking
Logging the same measurements each month shows whether a program is actually shifting composition, not just scale weight.
protect lean mass
Cutting goals
On a cut, the aim is to drop fat while keeping muscle — body fat % and lean mass tell you which one is actually moving.
FAQ
Common questions
It's a solid estimate — typically within about 3–4 percentage points of a DEXA scan for most people. It's far better than BMI for body composition because it accounts for waist and neck size, but it's a tape-measure formula, not a direct fat measurement. Use it to track change over time rather than as an exact clinical number.
Everyone needs height, neck, and waist. Women also need a hip measurement, because the female equation uses waist + hip − neck while the male equation uses only waist − neck. No scale is required for the percentage — weight is optional and only used to convert the percentage into lean body mass and fat mass.
Measure the neck just below the larynx (Adam's apple) with the tape sloping slightly down to the front. Men measure the waist around the navel; women measure at the narrowest point of the natural waist. Women also measure the hip around the widest part of the buttocks. Keep the tape snug but not compressing the skin, and measure on a normal breath out.
BMI only knows your height and weight, so it can't tell muscle from fat — a lean, muscular person and a person carrying excess fat can share a BMI. Body fat percentage estimates the actual fat fraction of your body, which is the number that drives composition goals and most health risk. BMI is a cheap population screen; body fat % is closer to what you actually care about.
Using the ACE categories, men are typically in the fitness range at 14–17%, average at 18–24%, and obese at 25%+, with essential fat as low as 2–5%. Women carry more essential fat: fitness is 21–24%, average 25–31%, and obese 32%+, with essential fat at 10–13%. Women's healthy ranges sit several points higher than men's by design.
Essential fat is the minimum the body needs for normal function — it cushions organs and supports hormones. Men need roughly 2–5%; women need roughly 10–13% because of reproductive and hormonal requirements. Dropping below the essential floor is unhealthy, which is why the female categories start higher than the male ones.
Small tape differences move the result a lot. A centimeter of difference at the waist, measuring after a meal, holding the tape at an angle, or breathing in versus out can all shift the estimate by a point or more. Measure at the same time of day, on bare skin, on a normal exhale, and take each measurement twice and average — consistency matters more than a single reading.
Once you have the body fat percentage and your weight, lean body mass is weight × (1 − fat% / 100) and fat mass is weight × (fat% / 100). For example, an 80 kg person at 20% body fat carries 16 kg of fat and 64 kg of lean mass. Enter your weight in the calculator and both figures appear automatically.
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Ugo CharlesBuilt and fact-checked against our editorial standards · Last updated June 2026
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