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 far off can this be?
Against DXA in 926 men and 481 women starting Army basic training, the U.S. military's circumference equations, the same tape-measure approach as the Navy method used here, read body fat 6.0 points low on average, give or take 3.5 points for men and 4.4 for women, and over 8 weeks of training they understated the change in men and missed it in women.
For the example inputs (a man, waist 85 cm, neck 38 cm, height 175 cm), the Navy method gives 16.9%. If the tape errs here as it did for those recruits, a DXA scan would most likely read about 22.9%, and for about two in three men between 19.4% and 26.4%.
The study measured young recruits; the size of the gap for older or very lean or very heavy people is not established. Use one method consistently to track change, and expect the tape to understate it.
Source: Foulis et al. 2023, Front Physiol, “Body composition changes during 8 weeks of military training are not accurately captured by circumference-based assessments” .
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.
- Expect a margin of several body-fat points. On the American Council on Exercise chart, 'fitness' is 14-17% for men and 21-24% for women, athletes 6-13% and 14-20%, and essential fat 2-5% and 10-13%.
- Most measurement errors come from the waist: measure at navel level while standing relaxed, not sucking in. Moving the tape higher or lower changes the reading by several points, so use the same landmark every time.
- 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
How do I measure body fat at home?
Pick one home method and repeat it the same way every 2-4 weeks. With a tape, measure neck and waist (and hips for women) at the same landmarks, standing relaxed, and enter them with your height here: that is the U.S. Navy method. With skinfold calipers, pinch the Jackson-Pollock sites (chest, abdomen and thigh for men; triceps, suprailiac and thigh for women); readings are inconsistent until the technique is practised. With a smart scale, weigh in the same state each time, in the morning before eating or drinking, because body water moves the reading. No home method matches a DEXA scan for a single reading, so follow the trend within one method and do not switch methods midway.
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?
Expect a rough estimate, not a scan-grade number. In 1,407 Army recruits, the military's circumference equations, which also use neck and waist, read about 6 body-fat points low against DEXA on average and missed most of the fat lost over 8 weeks of training (Foulis 2023). Skinfold equations carry an error of about 3 points even with a trained tester. Home bioimpedance scales vary most and shift with hydration: in one study their 95% limits of agreement with DEXA spanned about 14-15 percentage points (Li et al. 2013).
How accurate are body fat estimation methods?
DEXA is the usual reference, though it has its own measurement error. Hydrostatic weighing and air displacement (Bod Pod) come close to it. Skinfolds taken by a trained tester carry an error of about 3 body-fat points, and circumference equations like the Navy method used here can be further off: military circumference equations read about 6 points low against DEXA in 1,407 recruits (Foulis 2023). Home bioimpedance scales vary most and shift with hydration: in one study their 95% limits of agreement with DEXA spanned about 14-15 points (Li et al. 2013).
What is a healthy body fat percentage?
The American Council on Exercise's chart puts men at: essential fat 2-5%, athletes 6-13%, fitness 14-17%, average 18-24%, obese 25% and over; and women at: essential fat 10-13%, athletes 14-20%, fitness 21-24%, average 25-31%, obese 32% and over. Women carry more essential fat because of 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 same numbers as a table
- Reference Body fat by waist and neck circumference
Computed by this calculator's engine across common inputs, to cite or download as CSV.
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Background on the Body Fat Percentage Calculator
- Comparison How Accurate Is the Navy Body Fat Calculator vs Calipers
How accurate is the Navy body fat method? In 1,407 recruits, tape equations read 6 points low vs DXA and missed most fat loss; skinfolds erred by about 3.4.
- Statistics Body Composition Statistics: Body Fat & Lean Mass Norms
Body composition statistics: body fat at each BMI by sex and age, muscle mass by sex, how accurate each measurement method is, and the FFMI 25 line.
Articles
- 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.
- 11 min read Bod Pod vs DEXA vs Calipers: Body Fat Accuracy
Bod Pod runs about +/-2-3% body-fat error, DEXA +/-1-2%, calipers +/-3-4%. Compare accuracy, cost, and cadence to pick a body composition method for athletes.
- 7 min read BMI vs FFMI vs Body Fat: A 178cm/80kg Male Through Three Lenses
Run BMI, FFMI, and Navy body-fat on the same 178cm/80kg male. Where the BMI overweight flag clashes with FFMI 22, and what to actually believe.
By goal
Use it from an agent or code
Any agent can run this calculator by URL: put the inputs in the query string and get JSON back, with the inputs that used defaults and a line to cite (add format=md for markdown). MCP clients reach it through https://aifithub.io/mcp.
In code, import the same module; it runs where you import it, with no request or key.
import { compute } from "https://aifithub.io/engines/body-fat-percentage-calculator.js";Input and output contract, TypeScript types and the guide for agents.