Body Fat Percentage & Ideal Weight Calculator
Estimate body fat percentage with the US Navy circumference method, classify it by sex and age, and find ideal body weight with the Devine formula.
Body Fat Calculator — interactive calculator, computed instantly in your browser.
Body Fat Percentage Guide: US Navy Method, Classifications & Ideal Weight
Where BMI Stops, Body Fat Starts
Key Takeaway: BMI counts total mass; the US Navy circumference method estimates how much of that mass is fat using just neck, waist, and (for women) hip measurements.
Body fat percentage measures what portion of your total body weight is adipose tissue — unlike BMI, it distinguishes a muscular 90 kg athlete from a sedentary 90 kg office worker. The US Navy circumference method estimates it from three simple tape measurements, making it the most practical field test without calipers or water displacement.
1. The US Navy Formula
The Navy method uses a log₁₀ regression derived from thousands of DEXA scans:
- Neck: measured below the larynx, shoulders relaxed
- Waist: at the navel (men) or natural waist (women), relaxed breath
- Hip: widest point — required for women only
- All measurements in centimeters; accuracy ≈ ±3% vs. DEXA
2. Classification Ranges (ACE Guidelines)
- Men: <6% essential · 6–13% athletic · 14–17% fitness · 18–24% acceptable · 25%+ obese range
- Women: <14% essential · 14–20% athletic · 21–24% fitness · 25–31% acceptable · 32%+ obese range
- Women need 2–3% more essential fat for hormonal and reproductive health — do not chase male numbers
3. Ideal Body Weight (Devine Formula)
Alongside body fat, the calculator returns Devine ideal weight: 50 kg for men, 45.5 kg for women, plus 2.3 kg per inch over 5′0″. For a 175 cm man: 68.9 in − 60 = 8.9 in → 50 + 2.3 × 8.9 ≈ 70.4 kg. Treat it as a medical reference point, not a target — frame size and muscle mass shift it by 5–10 kg.
🔗 Body Composition Cross-References
BMI cannot separate fat from muscle, so the US Navy circumference method gives a practical body-fat estimate from three tape measurements. Explore our 💪 Health Hub for more body-metric tools.
Pair your body-fat result with BMI screening and daily calorie targets for a complete fitness picture.
Frequently Asked Questions (Body Fat Calculator)
It correlates within ±3% of DEXA scans for most people when measurements are taken correctly. It is less reliable for very muscular, obese, or elderly individuals, where calipers or DEXA are preferable.
For adults, 10–20% (men) and 18–30% (women) is generally healthy. Athletes run 6–13% (men) and 14–20% (women). Sustained essential-fat levels below 6% (men) or 14% (women) impair immune and hormonal function.
This is 'normal-weight obesity' — sufficient fat mass with low muscle. BMI has no body-composition component, so a sedentary person with visceral fat can score a normal BMI yet exceed 25% body fat. Strength training and protein intake address it.
Every 2–4 weeks, at the same time of day, before eating, using the same tape tension. Daily fluctuations are mostly water and glycogen — judge trends over months, not single readings.