How to use this calculator
Choose US or metric units and your sex, then enter your age, height, weight and these tape measurements:
- 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 waist.
- Hips (women only): around the widest part of the buttocks.
Measure on bare skin, standing relaxed, after a normal breath out. You’ll get your estimated body fat percentage, your fat mass and lean mass, your category on the American Council on Exercise (ACE) scale, a BMI-based estimate for comparison, your waist-to-height ratio, and how much fat you’d need to lose to reach the ACE fitness range.
The formulas
The US Navy equations were developed by James Hodgdon and Marcie Beckett at the Naval Health Research Center in 1984, by comparing circumference measurements with body fat measured by underwater weighing. In the inch-based form adopted by the Department of Defense, with every measurement in inches:
Men:
Women:
Metric measurements are converted to inches first. Fat mass is your weight × body fat %, and lean mass is everything else: muscle, bone, organs and water.
For comparison, the calculator also shows the Deurenberg estimate, published in the British Journal of Nutrition in 1991, which predicts body fat from BMI alone:
In the original study its standard error was 4.1 percentage points.
Worked examples
A man who is 5 ft 10 in (70 in) and 180 lb, with a 15.5-inch neck and a 35-inch waist:
- Waist − neck: 35 − 15.5 = 19.5 in
- 86.010 × log₁₀(19.5) − 70.041 × log₁₀(70) + 36.76 = 18.5% body fat
- Fat mass: 180 × 18.5% = 33.3 lb; lean mass 146.7 lb
That’s in the ACE “average” range for men. His BMI of 25.8 gives a Deurenberg estimate of 22.8%, about 4 points higher. To reach 17%, inside the fitness range, he’d need to lose about 3.2 lb of fat while keeping his lean mass.
A woman who is 5 ft 5 in (65 in) and 150 lb, with a 13.5-inch neck, 30-inch waist and 39-inch hips:
- Waist + hips − neck: 30 + 39 − 13.5 = 55.5 in
- 163.205 × log₁₀(55.5) − 97.684 × log₁₀(65) − 78.387 = 29.2% body fat
That’s “average” for women. Her BMI of 25.0 gives a Deurenberg estimate of 32.6%.
Body fat by waist size
How the Navy estimate changes with waist size, holding height and neck constant:
| Men: 5 ft 10 in, 15.5-in neck | Body fat | ACE category |
|---|---|---|
| 31-in waist | 9.9% | Athletes |
| 33-in waist | 14.4% | Fitness |
| 35-in waist | 18.5% | Average |
| 37-in waist | 22.1% | Average |
| 39-in waist | 25.5% | Obese |
| 41-in waist | 28.5% | Obese |
| Women: 5 ft 5 in, 13.5-in neck | Body fat | ACE category |
|---|---|---|
| 26-in waist, 36-in hips | 19.6% | Athletes |
| 28-in waist, 38-in hips | 25.3% | Average |
| 30-in waist, 39-in hips | 29.2% | Average |
| 32-in waist, 40-in hips | 32.9% | Obese |
| 34-in waist, 42-in hips | 37.6% | Obese |
Every inch of waist moves the result by roughly 2 percentage points, so a sloppy measurement can easily shift your category. Measure the same way, at the same time of day, each time.
Body fat categories
The categories shown on the scale are the general body fat ranges used by the American Council on Exercise:
| Category | 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% and higher | 25% and higher |
Women naturally carry more essential fat than men, which is why every range is higher. These ranges are broad guides for adults and don’t adjust for age.
How accurate is the tape method?
Circumference equations estimate body fat from body shape, so they inherit any error in your measurements and any difference between your build and the people the equations were developed on. A 2022 study by Potter and colleagues compared the circumference equations with DXA scans in 609 Marines. On average they underestimated men’s body fat by about 2.5 percentage points and overestimated women’s by 1 to 2 points, and individual results typically varied by around 4 points either way.
That’s good enough for tracking change over time, as long as you measure the same way each time. If you need a precise number, a DXA scan is the usual reference.
The military’s move away from tape tests
The Navy equations were used across the US military for decades. In June 2023, Army Directive 2023-11 switched the Army to a simpler one-site tape test using only the waist at the navel and body weight. The equations, as published in Army guidance, were:
- Men: %BF = −26.97 − (0.12 × weight in lb) + (1.99 × waist in inches)
- Women: %BF = −9.15 − (0.015 × weight in lb) + (1.27 × waist in inches)
That method didn’t last. In December 2025 a Department of Defense memo set a waist-to-height ratio under 0.55 as the upper limit for service body composition policies, and in July 2026 Army Directive 2026-13 made that ratio the Army’s only standard, rescinding the one-site test. The calculator shows your waist-to-height ratio alongside the 0.55 military limit for reference.
Using your result
Body fat percentage tells you more than weight or BMI alone, especially if you strength train. If you’re losing weight, the goal is to lose fat while keeping lean mass, which a falling body fat percentage confirms even when the scale is slow. The calorie deficit calculator sets a daily target for a goal weight, and the TDEE calculator can use your body fat percentage in the Katch-McArdle formula. To compare with a height-and-weight screen, see the BMI calculator.
Assumptions and limitations
- The equations were developed on adult military personnel and may be less accurate for people whose build differs from that group, such as older adults or very muscular people.
- Results depend heavily on measuring technique.
- They don’t apply to children, during pregnancy, or with fluid retention.
Sources
- Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy men from body circumferences and height. Report No. 84-11. San Diego, CA: Naval Health Research Center; 1984.
- Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy women from body circumferences and height. Report No. 84-29. San Diego, CA: Naval Health Research Center; 1984.
- Hodgdon JA, Friedl KE. Development of the DoD body composition estimation equations. Technical Document No. 99-2B. San Diego, CA: Naval Health Research Center; 1999.
- Potter AW, Tharion WJ, Holden LD, et al. Circumference-based predictions of body fat revisited: preliminary results from a US Marine Corps body composition survey. Front Physiol. 2022;13:868627.
- Deurenberg P, Weststrate JA, Seidell JC. Body mass index as a measure of body fatness: age- and sex-specific prediction formulas. Br J Nutr. 1991;65(2):105–114.
- American Council on Exercise. ACE Personal Trainer Manual (general body fat percentage categories).
- US Army Training Center and Fort Jackson Inspector General. IG Update 23-4: Army Directive 2023-11, Army Body Fat Assessment. 2023.
- Secretary of the Army. Army Directive 2026-13: Army Body Composition Program and Standards. 2026.
- Military Officers Association of America. Pentagon announces new approach to how the military will measure troops’ body fat. January 14, 2026.
These are estimates for general information, not a medical assessment. For a precise measurement or advice about your weight and health, talk to your doctor.
Frequently asked questions
How does the US Navy body fat method work?
It estimates body fat from circumference measurements and height. Men measure the neck and the waist at the navel; women measure the neck, the waist at its narrowest point and the hips. The equations, developed at the Naval Health Research Center in 1984, use the logarithm of those measurements to predict body fat percentage.
How accurate is the Navy body fat calculator?
It's a reasonable estimate, not a lab measurement. In a 2022 study of 609 Marines compared with DXA scans, the circumference equations underestimated men's body fat by about 2.5 percentage points on average and overestimated women's by 1 to 2 points, with individual errors of around 4 points either way. Careful, consistent measuring makes the biggest difference.
What is a healthy body fat percentage?
The American Council on Exercise puts average body fat at 18% to 24% for men and 25% to 31% for women, with fitness ranges of 14% to 17% and 21% to 24%. Essential fat, the minimum your body needs, is about 2% to 5% for men and 10% to 13% for women. These general ranges don't adjust for age.
Why is my BMI-based body fat estimate different?
The BMI-based Deurenberg formula only knows your height, weight, age and sex, so it can't tell muscle from fat or see where fat is stored. It tends to overestimate body fat in muscular people. The tape method uses your body shape, so the two often differ by a few percentage points.
Does the Army still use the tape test?
No. In 2023 the Army switched to a one-site tape test that used only the waist at the navel and body weight. In July 2026, Army Directive 2026-13 replaced it with a waist-to-height ratio standard. Soldiers must have a waist-to-height ratio under 0.55, and no tape-based body fat test can be used to challenge the result.
How should I measure my waist, neck and hips?
Use a flexible tape held level and snug against the skin without compressing it, and measure after breathing out normally. Measure the neck just below the Adam's apple, the waist at the navel (men) or the narrowest point (women), and the hips at the widest part of the buttocks. Take each measurement two or three times and use the average.
Updated November 2026. Results are estimates for educational purposes and depend on the inputs you provide.