Body composition
Body Fat Percentage Calculator
Estimate body fat percentage with the U.S. Navy tape-measure method, cross-checked against the BMI-based CUN-BAE formula, with your fat and lean mass.
Result
Where your body fat sits
Against the ACE categories for men.
Formula from Hodgdon & Beckett, U.S. Navy (1984), checked against the source on May 25, 2026.
What does the Body Fat Percentage Calculator calculate, and which formula does it use?
The Body Fat Percentage Calculator estimates body fat using the U.S. Navy circumference method: for men, 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450, and waist plus hip minus neck for women. With weight and age it adds the BMI-based CUN-BAE estimate (Gómez-Ambrosi 2012) as a cross-check and reports fat and lean mass, with the ACE category for your sex.
Last updated .
How to use it
- The Navy Method requires waist circumference (measured at navel level), neck circumference (just below the larynx), and for women, hip circumference (at the widest point). Use a flexible tape, not rigid. Measure twice and average.
- Your result has a ±3–5% margin. Healthy ranges: men 10–20%, women 18–28%. Athletic: men 6–13%, women 14–20%. Essential fat (minimum for organ function): men 2–5%, women 10–13%.
- Most measurement errors come from the waist: measure at navel level while standing relaxed — not sucking in. Measuring lower (at the hip) will underestimate body fat significantly.
- Body fat percentage tells you composition; BMI tells you mass relative to height. A muscular person will show normal/athletic body fat with an overweight BMI. Always compare both metrics.
- Track at the same time of day (morning, before eating) with consistent measurement positions. Single readings are unreliable — compare monthly averages of 3 consecutive morning measurements.
Questions people usually ask
What method does this body fat calculator use, and what measurements do I need?
It uses the U.S. Navy circumference method: enter height, neck and waist (men), plus hip for women, and it estimates body fat without calipers or a scan. When you also provide weight and age it adds the CUN-BAE estimate. This is a circumference method, not a skinfold-caliper method like Jackson-Pollock, so you only need a tape measure.
How accurate is the Navy circumference method compared with a DEXA scan?
The Navy circumference method this tool uses is typically accurate to within about 3-5%, versus roughly 1-2% for a DEXA scan (the gold standard, which needs equipment). Skinfold calipers in trained hands are also about 3-5%, while home bioelectrical-impedance scales are the least reliable at about 5-8% and vary with hydration.
How accurate are body fat estimation methods?
DEXA scan: ±1-2% (gold standard, requires equipment). Hydrostatic weighing: ±2-3%. BodPod (air displacement): ±2-3%. Skinfold calipers (trained user): ±3-5%. Bioelectrical impedance (home scales): ±5-8%, highly variable with hydration. This calculator uses the Navy Method (circumference-based), typically ±3-5%.
What is a healthy body fat percentage?
For men: essential fat 2-5%, athletic 6-13%, fitness 14-17%, average 18-24%, obese 25%+. For women: essential fat 10-13%, athletic 14-20%, fitness 21-24%, average 25-31%, obese 32%+. Women require higher essential fat due to hormonal and reproductive function.
Why does my body fat percentage seem high even though I exercise?
Exercise alone rarely produces large fat loss without a calorie deficit. Cardio burns 200-400 calories per session — easily offset by diet. Resistance training adds muscle but may not reduce fat significantly without dietary control. Fat loss requires a sustained calorie deficit regardless of exercise type.
How quickly can I reduce body fat percentage?
Sustainable fat loss is 0.5-1% of body weight per week. A 180 lb person can lose roughly 1-1.5 lb per week on a 500-750 calorie deficit. Faster loss accelerates muscle loss. Body fat percentage dropping 1-2 points per month is excellent progress; 3+ months is needed for visible changes.
The formula, worked through
- Formula Body Fat Percentage Formula (US Navy)
US Navy circumference-based body fat. Men: 86.010·log10(waist−neck) − 70.041·log10(height) + 36.76. Women: 163.205·log10(waist+hip−neck) − 97.684·log10(height) − 78.387.
- Formula BMI Formula
BMI = weight in kilograms divided by height in meters squared. Quick screening number, blind to body composition. Cutoffs are 18.5 / 25 / 30 (WHO).
- Formula Lean Body Mass Formula (Boer)
Lean body mass formula (Boer 1984). Male: LBM = 0.407·mass_kg + 0.267·height_cm − 19.2. Female: LBM = 0.252·mass_kg + 0.473·height_cm − 48.3.
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Background on the Body Fat Percentage Calculator
- Guide How to Measure Body Fat at Home: 4 Methods Compared
How to measure body fat at home: tape (Navy) method, skinfold calipers or a smart scale. Each misses DEXA by several points, so pick one and track the trend.
- Comparison How Accurate Is the Navy Body Fat Calculator vs Calipers
How accurate is the Navy body fat calculator? It reads within 3-4% of DEXA versus 2-3% for trained calipers. Navy wins on repeatability for solo tracking.
- Examples Body Fat Examples
Explore diverse real-world body fat examples, from sedentary professionals to athletes and new mothers, revealing unique insights into health, performance.
- Checklist Body Recomposition Checklist
Plan body recomposition with this actionable checklist. Simultaneously build muscle and burn fat through precise nutrition, effective training.
- Statistics Body Composition Statistics: Body Fat & Lean Mass Norms
Evidence-based body composition statistics: average body fat percentages, lean mass norms by sex and age, measurement accuracy, and natural FFMI ceilings.
- Learn What Is Body Fat Percentage? Definition & How It's Measured
Learn what body fat percentage means, how it's calculated, the methods used to measure it (DEXA, BIA, calipers), and why it beats weight or BMI for health.
Articles
- 10 min read Body Composition: The Four Lenses
Body composition through four lenses: BMI, FFMI, measured body fat, and energy balance. What each metric answers, where it fails, and the deep dives.
- 11 min read GLP-1 Muscle Loss: Keep Lean Mass with Lifting and Protein
GLP-1 weight loss costs lean mass: 25-39% of the total. How lifting 2-3x weekly and 1.2-1.6 g/kg protein hold muscle, and where the magnitude is debated.
- 13 min read Body Recomposition for Lifters: The Calorie Math
Body recomposition is real for specific populations under specific conditions. The four conditions, protein math scaled to LBM, 12-week example.
By goal
Use it from code
The same calculation as a JavaScript module you can import. It runs where you import it, with no request, key or rate limit.
import { compute } from "https://aifithub.io/engines/body-fat-percentage-calculator.js";Input and output contract, TypeScript types and the guide for agents.