Plot No. 42 · Health & Fitness
Body Fat Percentage Calculator
Estimate your body fat percentage from tape-measure readings using the US Navy method. It takes your height, neck and waist (plus hip for women) in centimetres, feeds them through a log10 circumference formula, and returns your body fat as a percentage with a fitness category.
This is a circumference-based estimate using the US Navy method, not a DEXA or skinfold measurement. It is an estimate, not medical advice.
The link saves your inputs so you can bookmark or share this exact result.
How body fat percentage is worked out
This calculator uses the US Navy circumference method, which estimates body fat from a few tape measurements rather than from a scale or a skinfold caliper. For men it takes height, neck and waist; for women it adds the hip measurement, because fat distribution differs. All measurements are entered in centimetres and the formula uses base-10 logarithms of the circumference differences.
For men the equation is 495 divided by (1.0324 minus 0.19077 times log10 of waist minus neck, plus 0.15456 times log10 of height), then minus 450. For women it is 495 divided by (1.29579 minus 0.35004 times log10 of waist plus hip minus neck, plus 0.22100 times log10 of height), minus 450. The result is mapped to a category band that is shifted higher for women, since healthy body fat is naturally greater.
How to use the body fat calculator
- Choose your sex, since men and women use different formulas and category bands.
- Enter your height, then your neck and waist measured in centimetres with a snug, level tape; women also enter the hip measurement.
- Read the body fat percentage and the fitness category, and re-measure on bare skin at the same time of day to track changes fairly.
Worked examples
Average-build man
Inputs: Male, height 178 cm, neck 38 cm, waist 92 cm
Result: About 21.5 percent body fat, which falls in the average range for men.
Woman with hip measurement
Inputs: Female, height 165 cm, neck 34 cm, waist 80 cm, hip 100 cm
Result: About 31.4 percent body fat, sitting in the average band for women.
Limitations and common mistakes
Edge cases and limitations
- It relies on circumferences, so it can read high for people who carry weight at the waist and low for very muscular or very lean bodies.
- Accuracy depends entirely on tape technique; a tape that is too tight, too loose or not level can move the result by several points.
- It is a screening estimate, typically within 3 to 4 points of a DEXA scan, not a clinical measurement.
Common mistakes
- Measuring the waist in the wrong place; men measure at the navel and women at the narrowest point, not wherever the trousers sit.
- For women, leaving out or guessing the hip measurement, which the female formula needs and which strongly affects the result.
Frequently asked questions
How does the US Navy body fat formula work?
It estimates body fat from body circumferences rather than skinfolds. For men it uses height, neck and waist; for women it adds the hip measurement. A 178 cm man with a 38 cm neck and 92 cm waist comes out at about 21.5 percent, which sits in the average range.
Where exactly do I measure?
Measure your neck just below the larynx, your waist at the navel for men and at the narrowest point for women, and your hips at the widest point. Keep the tape level and snug without compressing the skin, and measure on bare skin first thing in the morning for consistency.
How accurate is the tape method?
It is typically within about 3 to 4 percentage points of a DEXA scan for most people, which is good enough to track changes over time. It can read high on people with a fuller midsection and low on very lean or very muscular bodies, so treat it as a trend tracker rather than an exact figure.
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