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Summary
Body fat percentage is the proportion of your total body weight that is fat tissue. Unlike BMI, it distinguishes between fat and lean mass, making it a better indicator of health and fitness. The calculator estimates body fat using the US Navy circumference method, which requires only a tape measure and provides results within 3-4% of clinical methods like DEXA.
How it works
US Navy method
The US Navy developed a formula based on body circumference measurements:
Men: Body fat % = 86.010 x log10(waist - neck) - 70.041 x log10(height) + 36.76
Women: Body fat % = 163.205 x log10(waist + hip - neck) - 97.684 x log10(height) - 78.387
Measurements are in centimetres. Waist is measured at the navel, neck at the narrowest point, and hips at the widest point.
Body fat categories
| Category | Men | Women |
|---|---|---|
| Essential fat | 2-5% | 10-13% |
| Athletes | 6-13% | 14-20% |
| Fitness | 14-17% | 21-24% |
| Average | 18-24% | 25-31% |
| Obese | 25%+ | 32%+ |
Women carry higher essential fat due to reproductive function.
Other estimation methods
- Skinfold calipers (Jackson-Pollock 3 or 7 site): measures fat fold thickness at specific body sites. Accuracy depends on the tester’s skill.
- Bioelectrical Impedance (BIA): sends a small current through the body. Affected by hydration, food intake, and time of day.
- DEXA scan: clinical gold standard. Uses X-rays to measure bone, lean, and fat mass separately. Accuracy within 1-2%.
Worked example
Male: height 180 cm, waist 88 cm, neck 38 cm
- log10(88 - 38) = log10(50) = 1.6990
- log10(180) = 2.2553
- Body fat = 86.010 x 1.6990 - 70.041 x 2.2553 + 36.76
- = 146.14 - 157.93 + 36.76
- = 24.97% (Average category)
Inputs explained
- Gender — different formulas for men and women
- Height — in cm or feet/inches
- Waist circumference — measured at the navel
- Neck circumference — measured at the narrowest point
- Hip circumference — women only, measured at the widest point
Outputs explained
- Body fat percentage — estimated proportion of body weight that is fat
- Fat mass — body fat in kg
- Lean mass — everything else (muscle, bone, organs, water)
- Category — essential, athlete, fitness, average, or obese
- Comparison to healthy range — how far from the healthy range you are
Assumptions & limitations
- The Navy method has an accuracy of ±3-4% compared to DEXA. It is a screening tool, not a diagnostic measurement.
- Measurement consistency is key. Measure at the same time of day, same hydration level, and same anatomical landmarks.
- Formulas may be less accurate for very lean (bodybuilders) or very obese individuals.
- Does not distinguish between visceral fat (around organs, high health risk) and subcutaneous fat (under skin, lower risk).
- Muscle mass is not assessed — two people at the same body fat % can have very different muscle levels.
数据来源
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