Body Fat Calculator
| Fat mass | — |
|---|---|
| Lean mass | — |
| Body fat (BMI method) | — |
| BMI | — |
| Waist-to-height ratio | — |
Estimates only. Not a medical measurement.
Find out how much of your weight is fat with a soft tape and a few minutes. This body fat calculator uses the Navy circumference method: your height, neck, and waist, plus hips for women. You also get your waist-to-height ratio, and with your weight and age, fat mass, lean mass, and a BMI-based estimate.
Measurements
Body fat
16.5%
Body fat bands, men
16.5%
Pick Male or Female, then enter your height, neck, and waist, plus hips for women. Your body fat percentage appears at the top, and the bar under it marks your band: Essential, Athletes, Fitness, Average, or Obese. The bands follow the American Council on Exercise chart, which sets separate ranges for men and women.
Weigh-in
Lean: muscle, bone, water
Add your weight to see how it divides. Fat mass is your weight times your body fat percentage, the same sum the percentage calculator does. Lean mass is everything else: muscle, bone, water, and organs. When you're trying to lose fat, these two lines can show progress the scale alone hides.
Tape method
16.5%
Neck, waist, height
BMI method
22.8%
BMI 25.8, age 35
Fill in your age and weight, and a second number appears on the Body fat (BMI method) line, from a formula built on BMI, age, and sex (opens in a new tab). BMI uses only your height and weight, so it doesn't measure body fat directly (opens in a new tab) and can't tell muscle from fat. Treat this line as a second opinion: in the study behind it, the formula ran slightly high for people with obesity.
34 in ÷ 70 in
= 0.485
waist ÷ height
The last line divides your waist by your height. NICE (opens in a new tab), England's health guidance body, advises keeping your waist under half your height, a ratio below 0.5, as a simple check on health risk. It's also the only number the Army now uses, covered below.
Pick your country first to measure in inches or centimeters. Use a soft tape on bare skin, snug but not pressing in, and measure at the same time of day each time.
Wrap the tape just below your voice box (Adam's apple), sloping slightly down toward the front. Keep your chin level and your shoulders relaxed.
Men measure level with the navel. Women measure at the narrowest point between the ribs and the hips. Stand relaxed, breathe out normally, and don't pull your stomach in.
Women only: measure around the widest part of the buttocks, feet together. For men, the Hip box stays greyed out.
Stand against a wall without shoes for your height. Take each tape measurement two or three times and enter the average.
Want to calculate body fat for the Army? Since the July 2026 update (opens in a new tab), the Army doesn't measure body fat at all. It checks one number, your waist-to-height ratio, and the rules below come from the Army's own directive and worksheet.
Under Army Directive 2026-13 (opens in a new tab), the ratio is the only body composition measurement. The height and weight tables are discontinued, and soldiers are measured at least twice a year.
A ratio under 0.55 passes. At 0.55 or higher, a different team measures again the same day, and a soldier who still doesn't meet it is flagged and enrolled in the Army Body Composition Program.
The waist is taken at the belly button and rounded down to the nearest half inch, three times, then averaged. Height is rounded to the nearest half inch (DA Form 5500 (opens in a new tab)).
The Army records the ratio to three decimals and drops the rest, so 0.549888 counts as 0.549 and passes. The calculator shows the ratio the same way.
The old neck-and-waist tape test can't be used to challenge a ratio, and no Army Fitness Test score exempts a soldier from it.
Enter your height and the average of your three navel readings, both rounded the Army's way. The Waist-to-height ratio line fills in once your neck is entered too, plus your hips for women. Women: the body fat formula expects your narrowest waist, so treat this as a separate check and read only the ratio.
Pro
A soft tape and a few minutes are all it takes. There's no scan to book and no device to buy.
Pro
Measure the same spots at the same time of day, and you can follow the trend from month to month. One reading matters less than the direction it moves.
Pro
Your waist drives the result, and fat around the belly is the kind NICE (opens in a new tab) links to type 2 diabetes and heart disease. When your waist shrinks, the number follows.
Con
A tape pulled tight, or a waist taken a little too high, can move the result by a point or more.
Con
The men's formula reads only the neck and waist, so fat on the hips and thighs doesn't count. The women's formula adds the hips but still skips the arms and legs.
Con
The equations came from studies of U.S. Navy men and women in the 1980s. If your build is unusual, such as a thick neck from heavy training, the estimate can drift from your real number.
The calculator uses the circumference equations from 1984 U.S. Navy research (opens in a new tab). They estimate your body density from a few tape measurements, then turn density into a fat percentage. Here it's worked through for the man in the pictures.
Convert to centimeters
5 ft 10 in = 177.8 cm, the 15.5 in neck = 39.37 cm, and the 34 in waist = 86.36 cm.
Take the logs
Waist minus neck is 46.99 cm. log₁₀(46.99) = 1.6720, and log₁₀(177.8) = 2.2499.
Estimate body density
1.0324 − 0.19077 × 1.6720 + 0.15456 × 2.2499 = 1.0612.
Turn density into body fat
495 ÷ 1.0612 − 450 = 16.5%. The calculator keeps every digit, shows 16.5%, and splits 180 lb into 29.6 lb of fat and 150.4 lb of lean mass.
All you need is a soft tape. Measure your neck and waist, plus hips for women, then enter them with your height, and the calculator runs the Navy formula for you. The steps above show where to put the tape.
There's no single number. On the ACE chart, the Fitness band runs from 14% to just under 18% for men and from 21% to just under 25% for women. Average goes on to just under 25% for men and 32% for women, and anything at or above those is in the Obese band. This calculator uses the same bands at every age.
It gives an estimate, not a measurement. The equations predict body fat from group averages, so your result can sit a few points away from a lab scan such as DEXA, which the CDC (opens in a new tab) describes as a precise measure of body composition. It's most useful for tracking change, as long as you measure the same way each time.
Most smart scales use bioelectrical impedance: they send a weak current through your body and estimate fat from how easily it passes. That reading depends on how much water your body is holding, so being over- or under-hydrated (opens in a new tab) can throw it off. The tape method uses different inputs, so the two rarely match exactly. Compare each method only with itself.
Not with this calculator, since the main result needs your neck and waist. A piece of string works as a stand-in: wrap it, mark where it meets, and measure it against a ruler.
The Age box takes 18 to 99, because these formulas were built for adults. Children and teens change shape as they grow, and the BMI-based study (opens in a new tab) needed a separate formula for them.
Pentagon guidance dated December 2025 caps the ratio at under 0.55 for every service and calls for body composition checks twice a year (memo (opens in a new tab)). Each branch writes its own measuring rules, so check your service's current guide. The Waist-to-height ratio line here works as a practice check.
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Ratio CalculatorSimplify ratios, scale them, or solve A : B = C : D.A few tape measurements and your height are enough for a body fat percentage. Add your weight and age to see fat mass, lean mass, and the BMI method too. It's free, there's no sign-up, and your numbers stay in your browser.
