Body Fat Calculator (Navy, Skinfold, BMI)
Body-fat % four ways, with fat mass, lean mass and the healthy range for your age.
All methods with your measurements
| Method and typical accuracy | Body fat |
|---|
How it was calculated
For general information only, not medical advice. Consult a qualified health professional for advice about your situation.
About the Body Fat Calculator (Navy, Skinfold, BMI)
Body-fat percentage is the share of your weight that is fat. It says more than BMI because it separates fat from muscle, bone and water — but it is hard to measure without a scanner. This calculator gives four practical estimates you can take at home:
- the US Navy tape method (neck, waist and, for women, hips),
- the US Army one-site tape introduced in 2023 (waist at the navel and weight),
- Jackson-Pollock skinfolds (3 or 7 sites, with a caliper), converted with the Siri or Brozek equation,
- an estimate from BMI (Deurenberg).
For each you get body-fat %, fat mass and lean mass, how it compares with the healthy range for your age and sex (Gallagher et al.), and how accurate that method usually is. Enter more measurements to compare the methods side by side.
How to use it
- Enter your sex, age, weight and height (switch to lb · ft/in if you prefer).
- Choose a method. For the tape methods, measure with a flexible tape on bare skin, snug but not compressing, after breathing out normally.
- For skinfolds, pinch a fold of skin and the fat under it, measure it with a caliper and repeat each site at least twice, using the average.
- Read your body-fat %, fat and lean mass and the healthy range; the table compares every method you have measurements for.
Examples
Navy 18.8% · Army one-site 20.8% · From BMI 22.1% · Healthy range at 35: about 9–20%
Navy 27.7% (16.6 kg fat, 43.4 kg lean) · From BMI 28.6% · Healthy range at 30: about 21–33%
Density 1.0643 g/cm³ · Siri 15.1% · Brozek 15.2%
The equations
US Navy / Department of Defense (inches): 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. Men measure the abdomen at the navel; women measure the waist at its narrowest and the hips at their widest; the neck is measured just below the larynx.
US Army one-site (2023): men %BF = −26.97 − 0.12 × weight (lb) + 1.99 × abdomen (in); women %BF = −9.15 − 0.015 × weight (lb) + 1.27 × abdomen (in), with the abdomen measured at the navel.
Jackson-Pollock body density (skinfold sum S in mm, age in years): men 3-site (chest, abdomen, thigh) D = 1.10938 − 0.0008267 S + 0.0000016 S² − 0.0002574 age; women 3-site (triceps, suprailiac, thigh) D = 1.0994921 − 0.0009929 S + 0.0000023 S² − 0.0001392 age; 7-site (chest, midaxillary, triceps, subscapular, abdomen, suprailiac, thigh) men D = 1.112 − 0.00043499 S + 0.00000055 S² − 0.00028826 age, women D = 1.097 − 0.00046971 S + 0.00000056 S² − 0.00012828 age. Then Siri: %BF = 495 ÷ D − 450, or Brozek: %BF = 457 ÷ D − 414.2.
Deurenberg: %BF = 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4 (sex = 1 for men, 0 for women).
How accurate is each method?
- Skinfolds taken by a trained measurer have the smallest published error of these methods: the Jackson-Pollock equations have a standard error of about 3.4–3.9 percentage points. Measuring yourself is harder.
- US Navy tape: in a US Army study of about 1,900 soldiers measured against DXA scans, it read on average 4.8 points low for men and 1.7 points low for women, with a typical (root-mean-square) error of about 5.9 and 4.4 points.
- US Army one-site tape: in the same study the Army equation read about 3 points low on average — similarly for men and women and across ethnic groups — with a typical error of about 4.4 (men) and 4.6 (women) points. Florez et al., using circumferences from phone 3D scans and a four-compartment reference in 96 young adults, found limits of agreement of about ±9.5 points for individuals.
- From BMI: Deurenberg et al. report a standard error of 4.1 points; it slightly overestimates body fat in people with obesity and cannot tell a muscular person from one with more fat.
Use one method consistently to track change over time — trends are more reliable than any single reading.
Healthy body-fat ranges
Gallagher et al. linked body fat to the BMI cut-offs of 18.5, 25 and 30 using a prediction equation: %BF = 64.5 − 848 ÷ BMI + 0.079 × age − 16.4 × sex + 0.05 × sex × age + 39.0 × sex ÷ BMI (sex = 1 for men). The published table gives one range per 20-year age band; the calculator evaluates the equation at your exact age, so its limits can differ from the table by about a point (for a woman of 50 it gives 23–35%). The published ranges:
- Women — 20–39: healthy 21–33%, above 33–39%, high 39%+; 40–59: 23–34%, 34–40%, 40%+; 60–79: 24–36%, 36–42%, 42%+
- Men — 20–39: healthy 8–20%, above 20–25%, high 25%+; 40–59: 11–22%, 22–28%, 28%+; 60–79: 13–25%, 25–30%, 30%+
The ranges come from a 4-compartment model in mostly white adults. People of Asian descent tend to have more body fat at the same BMI (WHO expert consultation), so treat the ranges as a guide, not a diagnosis.
Where to measure skinfolds
- Chest: diagonal fold between the front of the armpit and the nipple
- Midaxillary: vertical fold on the side of the chest below the armpit, level with the bottom of the breastbone
- Triceps: vertical fold on the back of the upper arm, halfway between shoulder and elbow, arm relaxed
- Subscapular: diagonal fold just below the lower tip of the shoulder blade
- Abdomen: vertical fold about 2 cm to the side of the belly button
- Suprailiac: diagonal fold just above the hip bone, following its natural line
- Thigh: vertical fold on the front of the thigh, halfway between the top of the kneecap and the hip crease
Protocols differ slightly between textbooks; what matters most is using the same spots every time.
Sources
- McClung HL et al. Science behind policy: implementing a modern circumference-based body fat equation, Int J Obes 49:723-30 — DoD/Navy (Hodgdon) and 2023 Army equations as quoted from Army regulations, and their accuracy against DXA
- Florez CM et al. Body composition estimation from mobile phone three-dimensional imaging: evaluation of the USA Army one-site method, Br J Nutr 132:1143-51
- Jackson and Pollock (men) and Jackson, Pollock and Ward (women) skinfold equations, as given in PMC10453806 and PMC11374165
- Deurenberg P et al. Body mass index as a measure of body fatness, Br J Nutr 65:105-14
- Gallagher D et al. Healthy percentage body fat ranges, Am J Clin Nutr 72:694-701
Limitations
- All four methods are estimates. Laboratory methods (DXA, underwater weighing, four-compartment models) are needed for a precise figure.
- Tape and skinfold measurements change by a few points with small differences in technique — measure the same way, at the same time of day, each time.
- Not validated for pregnancy, children and teenagers, or very high levels of obesity (skinfolds become hard to pinch).
- Healthy ranges are given for ages 20–79 only.
Privacy
Everything happens in your browser. What you enter or open here is not uploaded or stored by MySmartCoPilot.
Frequently asked questions
Which body-fat method is most accurate at home?
Skinfolds taken carefully by a trained person are usually the most precise of these, followed by the tape methods. The BMI-based estimate is the least informative because it cannot tell muscle from fat. For tracking change, any method used consistently works better than switching between them.
What is a healthy body-fat percentage?
Using Gallagher et al.’s ranges, roughly 21–33% for women and 8–20% for men aged 20–39, rising a little with age (for example 24–36% for women and 13–25% for men aged 60–79). The calculator shows the range for your exact age.
Why is my Navy result different from my smart scale?
They work on different principles: bioimpedance scales estimate fat from how easily a weak current passes through the body, the tape method from body shape. In the US Army study both underestimated body fat compared with DXA scans, by different amounts — so a difference of a few points between methods is normal.
Where exactly do I measure my waist for the Army one-site method?
Around the abdomen at the level of the navel (belly button), with the tape horizontal, after a normal breath out. Use the same measurement for the Navy method if you are a man.
What is lean body mass?
Everything that is not fat — muscle, bone, organs and water. It is your weight minus your fat mass. Lean-mass-based BMR equations such as Katch-McArdle in the BMR calculator use it.