A body fat calculator estimates the share of your weight that is fat. This one uses the U.S. Navy tape method, which needs only your height and neck and waist measurements (plus hips for women). A man who is 70 inches tall with a 15-inch neck and 34-inch waist comes out at about 17.5% body fat.
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How to use the body fat calculator
- Choose your sex and unit system, and enter your age and weight.
- Enter your height, neck and waist; women also enter hips.
- Read your Navy body fat %, category, fat mass and lean mass.
- Compare it with the BMI-based estimate shown below the result.
Body fat calculator formula (U.S. Navy method)
The Navy method estimates body fat from height and tape measurements. With all measurements in inches:
- Men: body fat % = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76
- Women: body fat % = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387
With centimetres, the body fat calculator uses the equivalent metric form: men 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450; women 495 ÷ (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450.
Body fat calculator worked examples
| Person | Measurements | Navy body fat |
|---|---|---|
| Man | height 70 in, neck 15 in, waist 34 in | 17.51% |
| Woman | height 65 in, neck 13 in, waist 30 in, hip 40 in | 31.09% |
For the man: 86.010 × log10(19) − 70.041 × log10(70) + 36.76 ≈ 17.5%. If he weighs 180 lb, his fat mass is about 31.5 lb and his lean mass about 148.5 lb.
Body fat categories
The body fat calculator labels your result with the American Council on Exercise (ACE) ranges:
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Obese | 25% or more | 32% or more |
It also shows a second estimate from BMI and age (the Deurenberg equation: 1.20 × BMI + 0.23 × age − 16.2 for men, − 5.4 for women), plus a Jackson-Pollock “ideal” body fat for your age.
How to measure for the tape method
- Neck: just below the larynx (Adam’s apple), with the tape sloping slightly down toward the front.
- Waist: men at the navel; women at the narrowest point of the abdomen.
- Hip (women): around the widest part of the buttocks.
- Stand relaxed, do not suck in, keep the tape level and snug without compressing the skin, and take each reading two or three times.
A 1-inch error in the waist changes the result by roughly 2 to 3 percentage points, so careful measuring matters more than decimals.
How accurate is the Navy method?
Tape methods are quick estimates. They work best for tracking change in the same person over time, measured the same way. Results can differ by several points from DEXA scans or other lab methods, especially at the high and low ends. The U.S. Army replaced its neck-and-waist tape test with a one-site abdominal measurement in 2023, and DoD rules now let each service choose its own method, so this calculator may not match a current military standard. The CDC notes that BMI and waist size are screening tools rather than diagnoses.
For education only, not medical advice. Ask a clinician about your health and body composition.
Tracking changes over time
A single body fat reading is less useful than a trend. Measure under the same conditions each time, ideally in the morning before eating, and repeat every four weeks rather than daily, because tape measurements move with water and posture.
Splitting weight into fat and lean mass shows what a change really means. At 85 kg and 25% body fat, a person carries about 21.3 kg of fat and 63.8 kg of lean mass. If they reach 81 kg at 22%, fat is about 17.8 kg and lean mass about 63.2 kg. Most of the 4 kg lost was fat, which is the goal. If the body fat calculator showed the percentage unchanged after a large weight loss, much of it would have been muscle or water, and a review of protein intake and strength training would make sense.
Related converters and calculators
Related tools:
- Army body fat calculator: one-site tape test
- BMI calculator: weight for height
- Lean body mass calculator: fat-free mass
- BMR calculator: resting calories
- Ideal weight calculator: weight ranges
Sources
U.S. Army: New Army Body Composition Program (2023); CDC: Assessing your weight.
Questions about this calculator
How accurate is the Navy body fat method?
It is an estimate. Results can differ by several percentage points from lab methods such as DEXA; it is most useful for tracking change over time.
Where do I measure my waist?
Men measure at the navel. Women measure at the narrowest part of the abdomen.
What is a healthy body fat percentage?
ACE lists 18–24% as average for men and 25–31% for women; fitness ranges are 14–17% and 21–24%.
Why do women enter a hip measurement?
The women’s Navy equation uses waist plus hip minus neck because women carry more fat on the hips.
Does the military still use this formula?
The Army switched to a one-site abdominal tape test in 2023. DoD lets each service choose its method, so check your service’s current rules.
Check the assumptions and units before relying on a result. Financial, tax and health estimates do not replace advice for your individual circumstances.
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