How this body fat calculator works
U.S. Navy method (primary): Circumference equations from Hodgdon and Beckett (Naval Health Research Center, 1984) using neck, waist, and (for women) hip with height. It reflects body shape more than BMI alone.
BMI method (secondary): Estimates body fat from BMI, age, and sex using published linear formulas (adults and children/teens use different coefficients). Convenient but less specific than tape measurements.
Neither replaces DEXA, hydrostatic weighing, or skilled skinfold testing for clinical precision.
How to measure correctly
Use a flexible tape; measure to the nearest ¼ inch or 0.5 cm.
- Waist — men: horizontal around the navel, relaxed (do not suck in).
- Waist — women: narrowest natural waist (usually above the navel).
- Neck: just below the larynx; tape slightly sloping toward the front; shoulders relaxed.
- Hip — women only: largest horizontal circumference around hips and buttocks.
Body fat categories (ACE)
| Description | 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%+ | 25%+ |
Essential fat supports hormones and organs. Athletes and fitness ranges reflect training and lifestyle. Average is common in the general population; obese ranges align with higher metabolic and cardiovascular risk and warrant professional guidance.
Jackson & Pollock ideal body fat by age
Ideal targets rise modestly with age. This calculator interpolates between the standard age nodes.
| Age | Women | Men |
|---|---|---|
| 20 | 17.7% | 8.5% |
| 25 | 18.4% | 10.5% |
| 30 | 19.3% | 12.7% |
| 35 | 21.5% | 13.7% |
| 40 | 22.2% | 15.3% |
| 45 | 22.9% | 16.4% |
| 50 | 25.2% | 18.9% |
| 55 | 26.3% | 20.9% |
What is body fat?
Adipose tissue stores energy as fat, secretes hormones (e.g. leptin, adiponectin), cushions organs, and helps insulate the body. Fat-soluble vitamins (A, D, E, K) need dietary fat for absorption.
Essential vs storage fat
Essential fat is required for life and reproduction — higher in women. Storage fat includes subcutaneous fat under the skin and visceral fat around organs. Excess visceral fat is especially tied to insulin resistance, inflammation, and cardiovascular risk.
Formulas (reference)
USC = inches; SI = centimeters for circumferences and height.
- Navy — men (USC): BFP = 86.010×log₁₀(waist − neck) − 70.041×log₁₀(height) + 36.76
- Navy — women (USC): BFP = 163.205×log₁₀(waist + hip − neck) − 97.684×log₁₀(height) − 78.387
- Fat mass: weight × (BFP ÷ 100). Lean mass: weight − fat mass.
- BMI method — adult men: BFP = 1.20×BMI + 0.23×age − 16.2
- BMI method — adult women: BFP = 1.20×BMI + 0.23×age − 5.4
- BMI method — boys: BFP = 1.51×BMI − 0.70×age − 2.2
- BMI method — girls: BFP = 1.51×BMI − 0.70×age + 1.4
Other measurement methods
- DEXA — detailed bone, fat, and lean mass; often considered a gold standard for research and clinics.
- Hydrostatic weighing and Bod Pod — density-based; accurate with good protocol.
- BIA (scales/handheld) — convenient; accuracy varies with hydration and device quality.
- Skinfold calipers — depend strongly on tester skill and site selection.
Health context
Excess adiposity, especially visceral fat, is associated with higher risks of cardiovascular disease, type 2 diabetes, sleep apnea, some cancers, and joint load. WHO and CDC track obesity trends because of population-level health impact. If you have concerns, discuss targets and plans with a qualified clinician.
See also: BMI Calculator · Calorie Calculator.