Body fat percentage by the US Navy tape method, Jackson-Pollock 3- or 7-site skinfolds, or from BMI, with fat and lean mass and the ACE category.
By AdminDrafted with AI writing toolsUpdated Checked examples: 8
By the US Navy circumference method you carry about 16.9 % body fat (11.9 kg of fat and 58.1 kg of lean mass), which ACE classes as “Fitness”.
This is the metric form; the original inch-based Hodgdon–Beckett regression gives results a few tenths of a percent different.
The ACE category is read from the value rounded to 0.1 %.
Body fat percentage is the share of body weight that is fat. The US Navy method (Hodgdon and Beckett, 1984) uses the logarithms of height and of waist minus neck, with the hip added for women. The Jackson-Pollock methods turn a sum of 3 or 7 caliper skinfolds and age into body density, which the Siri equation converts with %BF = 495 ÷ density − 450. The Deurenberg method estimates it from BMI, age and sex. Fat and lean mass follow from your weight.
People use it to follow changes in body composition that weight and BMI miss. With the defaults, a man 175 cm tall with a 38 cm neck and an 85 cm waist comes out at 16.9 % body fat, 11.9 kg of his 70 kg, which the American Council on Exercise (ACE) classes as fitness.
Each method is a regression fitted on adult samples, so a single reading can differ from a laboratory measurement by several percentage points. Repeat readings are comparable only when they use the same method and measurement sites.
Body fat percentage is fat mass divided by body weight. Outside a lab it is estimated from a tape measure (US Navy), skinfold calipers (Jackson-Pollock) or BMI and age (Deurenberg). For a 30-year-old man of 70 kg and 175 cm, four methods give 14.5 % to 18.1 %.
The rows below put one set of measurements through the men's and then the women's equations:
| Method | Formula sex | Body fat | Fat mass, kg | ACE label |
|---|---|---|---|---|
| Navy metric | Male | 16.9% | 11.9 | Fitness |
| JP 3-site | Male | 14.5% | 10.1 | Fitness |
| JP 7-site | Male | 14.9% | 10.4 | Fitness |
| BMI estimate | Male | 18.1% | 12.7 | Average |
| Navy metric | Female | 27.8% | 19.5 | Average |
| JP 3-site | Female | 19.1% | 13.3 | Athletes |
| JP 7-site | Female | 20.9% | 14.7 | Athletes |
| BMI estimate | Female | 28.9% | 20.2 | Average |
The label is the American Council on Exercise (ACE) category, and it can change with the method. Through the women's equations, the same body is Athletes by skinfold but Average by tape or BMI, up to almost 10 points apart.
Switching methods between readings can also fake progress. Going from the BMI estimate to the 3-site skinfold would show the man with 2.5 kg less fat and nothing changed.
Any of these estimates can feed the Katch-McArdle equation in the BMR and TDEE calculator.
The US Navy method predicts body fat from height and a few tape measurements, using equations Hodgdon and Beckett fitted to Navy personnel in 1984. A woman 168 cm tall with a 33 cm neck, 76 cm waist and 100 cm hips comes out at 29.1 % body fat.
Both equations use base-10 logarithms of measurements in centimeters:
The bracketed part predicts body density. The outer "495 ÷ … − 450" is the Siri equation, which turns that density into a fat percentage. Age plays no part in either equation.
The woman above weighs 64 kg.
Skinfold equations predict body density from the summed thickness of pinched folds of skin and the fat under them, plus age. The Siri step then converts density to a percentage, as in the Navy method.
| Method | Men | Women |
|---|---|---|
| 3-site | Chest, abdomen, thigh | Triceps, suprailiac, thigh |
| 7-site | Chest, midaxillary, triceps, subscapular, abdomen, suprailiac, thigh | Same seven sites |
With S the sum of the folds in millimeters and A the age in years, the density equations are:
A 35-year-old man with a 14 mm chest, 24 mm abdominal and 18 mm thigh fold has S = 56 mm. His density is 1.10938 − 0.04630 + 0.00502 − 0.00901 = 1.05909, and 495 ÷ 1.05909 − 450 = 17.4 % body fat.
The men's equations were fitted on 308 men aged 18 to 61 and cross-checked on 95 more. The women's came from 249 women aged 18 to 55, and their authors advised care with women over 40.
For the woman in the Navy example, a 1 cm error at the waist, hip or neck shifts the result by about half a percentage point. A 1 cm error in height shifts it by about a quarter:
| Measurement off by +1 cm | New body fat | Change |
|---|---|---|
| Waist | 29.62 % | +0.49 points |
| Hip | 29.62 % | +0.49 points |
| Neck | 28.63 % | −0.49 points |
| Height | 28.86 % | −0.26 points |
Calipers are just as sensitive. Reading each of the man's three folds 1 mm thicker raises his result from 17.4 % to 18.2 %, moving him from the American Council on Exercise (ACE) Fitness band to Average.
With a tape, measure on bare skin, at the same time of day, after a normal breath out. Take the neck just below the larynx and the hips at the widest point of the buttocks. Men measure the waist at the navel, women at its narrowest point.
With calipers, the standards summarized in a 2026 review of skinfold protocols agree on six points:
The same review found that standards disagree on where some sites are. The abdominal fold is taken 2, 3 or 5 cm to the side of the navel, vertical in some standards and horizontal in others.
Pick one written protocol, keep to it, and have the same person measure each time.
ACE's categories use the same bands at every age. The most widely used age-specific ranges come from Gallagher and colleagues (2000), who measured 1,626 adults in the UK, US and Japan with DXA and four-compartment models.
They worked out the body fat that corresponds to a BMI of 18.5, 25 and 30 at each age. For white adults, as tabulated by Colombo and colleagues (2008):
| Age | Women: healthy | Women: obese from | Men: healthy | Men: obese from |
|---|---|---|---|---|
| 20 to 39 | 21 to 33 % | 39 % | 8 to 21 % | 26 % |
| 40 to 59 | 23 to 35 % | 41 % | 11 to 23 % | 29 % |
| 60 to 79 | 25 to 38 % | 43 % | 13 to 25 % | 31 % |
Values between the healthy upper limit and the obese threshold correspond to a BMI of 25 to 29.9. The paper gives separate figures for African American and Asian adults, and its authors called the ranges provisional.
The two systems can disagree. The woman in the Navy example, at 29.1 %, is Average by ACE and inside Gallagher's healthy range at any age.
A 65-year-old woman at 36 % is Obese by ACE, whose obese band starts at 32 % for women. By Gallagher she sits inside the healthy range of 25 to 38 % for her age.
For lean mass from height and weight alone, use the lean body mass calculator. The Army body fat calculator applies the Army's 2026 waist-to-height standard.
Checked against: 495 / (1.0324 − 0.19077·log10 48 + 0.15456·log10 178) − 450 = 17.2039; 80 × 17.2039 % = 13.763 kg; ACE men fitness 14–17 %
Checked against: 495 / (1.29579 − 0.35004·log10 134 + 0.22100·log10 165) − 450 = 25.3755
Checked against: Metric form after ×2.54 conversion = 17.4347; Hodgdon–Beckett inch form gives 17.513
Checked against: 1.10938 − 0.0008267·45 + 0.0000016·45² − 0.0002574·30 = 1.0676965; Siri 495/D − 450 = 13.6149
ACE's reference ranges put average at 18–24 % for men and 25–31 % for women, fitness at 14–17 % and 21–24 %, and athletes at 6–13 % and 14–20 %. Obese starts at 25 % for men and 32 % for women. Essential fat, the minimum needed for normal physiological function, is 2–5 % for men and 10–13 % for women. These are fitness-industry reference bands, not clinical diagnostic cut-offs.
Their standard errors are about 3 to 4 percentage points of body fat. Each formula was fitted against underwater weighing: the Jackson-Pollock men's equations had a standard error of 0.0073 g/ml in body density (about 3 points of body fat), the women's 3.6 to 3.8 points, and Deurenberg's BMI formula 4.1 points. Laboratory methods such as underwater weighing and DXA scans remain the reference.
Use a non-stretch tape that sits snug on the skin without compressing it. Measure the neck just below the larynx and the waist at the navel for men or at the narrowest point for women; women also measure the hips at the widest point of the buttocks. Averaging three readings per site helps, because at the defaults a 1 cm change in waist moves the result by about 0.8 percentage points.
BMI divides weight by height squared and says nothing about what the weight is made of, while body fat percentage estimates the share that is fat. An 80 kg, 178 cm man has a BMI of 25.2 whatever his build; Deurenberg's formula puts a 40-year-old at 23.3 % fat, but a muscular man of the same size measures far lower by tape or calipers. In Deurenberg's 1991 data, BMI with age and sex explained 79 % of the variation in measured body fat.
For information only, not medical advice. These formulas describe populations, not you; talk to a clinician before acting on a result.
This calculator includes 8 worked examples with independently sourced answers. They run in the test suite, and you can run them here too.