Body fat
calculator.
Estimate your body fat percentage from height and a tape measure, using the circumference equations the U.S. military has used since 1984. You also get fat and lean mass, a second estimate from BMI and age, and the official DoD rounding rules if you want to check a tape test.
By the circumference (U.S. Navy / DoD) method, body fat is about 20.4%: 36.6 lb of fat and 143.4 lb of lean mass. The BMI-based estimate is 24.0%.
- Body fat (circumference method)
- 20.4%
- Fat mass
- 36.6 lb
- Lean mass (everything except fat)
- 143.4 lb
- Body fat (BMI-based estimate)
- 24.0%
- BMI
- 25.8 kg/m²
- Circumference value (abdomen − neck)
- 20.5 in
%BF = 86.010 × log10(abdomen − neck) − 70.041 × log10(height) + 36.76 = 86.010 × 1.31175 − 70.041 × 1.8451 + 36.76 = 20.35% (inches); BMI estimate = 1.20 × 25.83 + 0.23 × 40 − 10.8 − 5.4 = 23.99%A tape measure,
two logarithms.
- Men: %BF = 86.010 × log10(abdomen − neck) − 70.041 × log10(height) + 36.76. Women: %BF = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387. All in inches, as published in DoD Instruction 1308.3 (2002), from Hodgdon and Beckett (1984).
- Centimeters are converted to inches exactly (1 in = 2.54 cm), so metric and U.S. entries of the same body give the same answer.
- “DoD tape-test rules” rounds height to the nearest ½ inch, the neck up and the abdomen, waist and hip down to the ½ inch, then the result to a whole percent, the way the DoD look-up tables do. “Exact” uses your numbers as typed and shows one decimal.
- Fat mass = weight × body fat ÷ 100; lean mass is the rest. The second estimate is Deurenberg’s adult equation: 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4, with men = 1 and women = 0.
- Adults 18 and over. An estimate for information only, not a diagnosis, and not an official military assessment.
How do you calculate body fat with the Navy method?
Measure your height, your neck just below the Adam’s apple, and your abdomen at the navel (men) or your waist at its narrowest plus your hips at their widest (women). Subtract the neck from the abdomen, or from waist plus hip, and put that number and your height into the equation for your sex. A man 70 inches tall with a 15.5-inch neck and a 36-inch abdomen has a circumference value of 20.5 inches, so his estimate is 86.010 × log10(20.5) − 70.041 × log10(70) + 36.76 = 86.010 × 1.31175 − 70.041 × 1.84510 + 36.76 = 20.4%.
The method needs only a tape measure, which is why the armed forces adopted it. In the DoD’s words, the equations “rely heavily on assessment of abdominal fat”; the neck and height adjust for body size. Measure each site three times on bare skin, with the tape level and snug but not pressing in, and use the average.
Men: %BF = 86.010 × log10(abdomen − neck) − 70.041 × log10(height) + 36.76
Women: %BF = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387
(all in inches)How do women measure for the Navy body fat formula?
Women use three sites. Measure the neck just below the larynx, the natural waist at its narrowest (usually halfway between the navel and the bottom of the breastbone), and the hips around the widest part of the buttocks seen from the side. For a woman 64 inches tall with a 13-inch neck, a 29-inch waist and 38-inch hips, the circumference value is 29 + 38 − 13 = 54 inches and the estimate is 163.205 × log10(54) − 97.684 × log10(64) − 78.387 = 27.9%. At 140 lb that is 39.1 lb of fat and 100.9 lb of lean mass.
How does the military round tape test measurements?
The 2002 DoD instruction that published these equations records every circumference to the nearest half inch, but rounds the neck up and the abdomen, waist and hip down. Its own examples are a 13⅜-inch neck recorded as 13½, a 28⅝-inch waist as 28½ and a 44⅜-inch hip as 44. Height is recorded to the nearest half inch and the result to a whole percent, “erring on the side of the Service member”. A woman 64¾ inches tall with those three measurements is scored on 65 inches and 28.5 + 44 − 13.5 = 59 inches: 33.53%, recorded as 34%.
Choose “DoD tape-test rules” to apply these steps. We checked them against 40 cells of the DoD look-up tables, and the calculator reproduces every one. Each service now runs its own program under DoD Instruction 1308.03 (2022), so its current regulation decides how an official test is done.
How do you estimate body fat from BMI?
Deurenberg, Weststrate and Seidell (1991) fitted body fat measured by densitometry in 1,229 people to BMI, age and sex. For adults: body fat % = 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4, with men = 1 and women = 0. The 40-year-old man above, at 180 lb and 70 inches, has a BMI of 25.83, so his estimate is 1.20 × 25.83 + 0.23 × 40 − 10.8 − 5.4 = 24.0%, against 20.4% by tape.
The equation’s standard error is 4.1 percentage points, and the authors found it slightly overestimates body fat in people with obesity. Because BMI cannot tell muscle from fat, it reads high for muscular people. The calculator shows it as a second opinion: if the two estimates are far apart, the tape result is usually the better guide.
BF% = 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4 (men = 1, women = 0)How do you calculate fat mass and lean mass from body fat percentage?
Multiply your weight by the body fat fraction to get fat mass. The remainder is lean mass, which includes muscle, bone, organs and water. At 180 lb and 20.35% body fat, fat mass is 180 × 0.2035 = 36.6 lb and lean mass is 180 − 36.6 = 143.4 lb. To estimate lean mass from height and weight alone, use the lean body mass calculator.
What body fat percentage do the armed forces allow?
DoD Instruction 1308.03 (2022) lets each service set its own maximum, within limits: no stricter than 18% and no more lenient than 26% for men, and no stricter than 26% and no more lenient than 36% for women. Those are fitness-for-duty standards, not health targets, and many services also screen by weight or waist-to-height ratio first. The calculator shows them only for comparison. It does not label your result as healthy or unhealthy, because there is no single agreed medical cut-off for body fat percentage.
Worked examples.
Man, U.S. units
40-year-old man, 5 ft 10 in, 180 lb, neck 15.5 in, abdomen 36 in.
20.4%: 36.6 lb of fat and 143.4 lb of lean mass; BMI estimate 24.0%.
Load this exampleWoman, U.S. units
30-year-old woman, 5 ft 4 in, 140 lb, neck 13 in, waist 29 in, hip 38 in.
27.9%: 39.1 lb of fat and 100.9 lb of lean mass; BMI estimate 30.3%.
Load this exampleMan, metric
25-year-old man, 178 cm, 70 kg, neck 50 cm, waist at the navel 96 cm.
15.7%: 11.0 kg of fat and 59.0 kg of lean mass; BMI estimate 16.1%.
Load this exampleTape test with DoD rounding
Woman, 64¾ in, 150 lb, age 30; neck 13⅜, waist 28⅝, hip 44⅜ in (the DoD instruction’s own measurement examples).
34% (33.53% before rounding), scored on 65 in, neck 13½, waist 28½ and hip 44 in.
Load this exampleMetric tape test with DoD rounding
Man, 180 cm, 80 kg, age 30; neck 40.3 cm, abdomen 94.2 cm.
21%: scored on 71 in, neck 16 in and abdomen 37 in, the DoD table value for those measurements.
Load this exampleWhat this calculator
does not do.
- It is an estimate, not a measurement. The equations come from studies of U.S. Navy men and women, and one person’s result can be off by several percentage points. Careless tape placement adds more error than the equation does.
- It is for adults 18 and over. It does not apply to children or during pregnancy, and it is less reliable for very muscular or very lean people.
- It is not an official military body composition assessment. Each service sets its own procedures and standards under DoD Instruction 1308.03, and some now use other methods.
- Information only, not medical advice or a diagnosis. Talk to a clinician about what your body composition means for your health.
Common questions.
How accurate is the Navy body fat calculator?
It estimates body fat from circumferences, so it can be a few percentage points away from a laboratory measurement for one person. The DoD credits the method with small measurement error when sites are taped correctly. For a direct measurement, use a DXA scan or underwater weighing.
Where do I measure my waist for the Navy method?
Men measure the abdomen level with the navel, at the end of a normal breath out. Women measure the natural waist at its narrowest point, usually halfway between the navel and the bottom of the breastbone, and add a hip measurement.
Can I use centimeters?
Yes. Choose “Centimeters and kg”. The calculator converts to inches exactly and uses the same equation, so the answer is identical to entering inches.
Why is my BMI body fat estimate different?
The BMI estimate uses only height, weight, age and sex. It cannot see where your weight is, so it reads high for muscular people and is less precise, with a standard error of 4.1 percentage points.
Is this the Army tape test?
Not necessarily. These are the equations the DoD prescribed for all services in 2002, widely known as the Navy method. Since 2022 each service sets its own procedure, so check your service’s current regulation for an official result.
- DoD Instruction 1308.3, DoD Physical Fitness and Body Fat Programs Procedures (November 5, 2002), Enclosure 3 — the published male and female equations in inches, measurement sites and techniques, half-inch rounding rules, look-up tables E3.T1 and E3.T2, and citation of Hodgdon and Beckett (1984). Cancelled in 2022; archived copy
- DoD Instruction 1308.03, DoD Physical Fitness/Body Composition Program (March 10, 2022) — current policy: services may use body fat, waist-to-height ratio, abdominal circumference or height-weight screening; body fat standards between 18 and 26% (men) and 26 and 36% (women). It does not print an equation
- 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;65:105–114 — adult equation BF% = 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4, SEE 4.1%; 1,229 subjects aged 7–83; slight overestimate in obesity
Body fat comes from the DoD equations in inches, as printed in DoD Instruction 1308.3. Metric values are converted to inches exactly, so U.S. and metric entries of the same body agree. The optional DoD mode applies the instruction’s half-inch rounding and rounds the result to a whole percent. Our tests check 40 cells drawn at random from the instruction’s own look-up tables and reproduce every one. They also check five cases worked separately in 40-digit decimal arithmetic, including calculator.net’s default case and the instruction’s rounding examples. Further tests cover 300 random bodies for unit invariance, monotonicity and the fat and lean mass split, validation of every field, and 500 extreme-input cases.
Built and reviewed by CalculatorLab against the sources above; every worked example on this page is re-checked by our automated test suite before each release. How we build and check calculators. Found a problem? Tell us.