Body Fat Calculator
Estimate body fat percentage with the US Navy method.
Measured around the neck, just below the larynx.
At the navel.
Estimated body fat
- Category
- Fitness
An estimate from the U.S. Navy circumference method, not a clinical measurement like a DEXA scan. Measure snugly without compressing the skin, and discuss results with a clinician.
How the body fat calculator works
This tool estimates your body fat percentage from a few tape measurements using the U.S. Navy circumference method. It is the same approach the Navy uses for body composition screening, and it needs only a tape measure, not calipers or a scale.
The method fits your measurements to a formula based on base-10 logarithms. The inputs differ by sex because fat is distributed differently:
- Men:
495 / (1.0324 - 0.19077 * log10(waist - neck) + 0.15456 * log10(height)) - 450 - Women:
495 / (1.29579 - 0.35004 * log10(waist + hip - neck) + 0.22100 * log10(height)) - 450
All measurements are taken in centimetres. If you enter inches, the calculator converts them first using the exact factor 1 in = 2.54 cm, so both unit systems give the same answer. The men’s formula depends on how far the waist exceeds the neck, which is why your waist must be larger than your neck for a result to exist.
The estimate is then sorted into descriptive categories from the American Council on Exercise, which differ by sex. For men: athletes 6 to 13 percent, fitness 14 to 17, average 18 to 24. For women the same labels sit higher, reflecting the essential fat women carry.
Worked example
Take a man who is 180 cm tall with a 40 cm neck and an 85 cm waist.
- Waist minus neck:
85 - 40 = 45 - Denominator:
1.0324 - 0.19077 * log10(45) + 0.15456 * log10(180) = 1.0324 - 0.3155 + 0.3490 = 1.0659 - Body fat:
495 / 1.0659 - 450 = 14.5%
That lands in the fitness band. If his waist were 80 cm instead of 85, the estimate would drop to 10.3%, into the athletes range, which shows how sensitive the number is to waist girth.
Now a woman who is 165 cm tall with a 34 cm neck, 75 cm waist, and 95 cm hips. Plugging into the women’s formula gives 26.4%, which sits in the average band.
The same answers come out in imperial. A man 71 in tall with a 15 in neck and 34 in waist converts to roughly 180.3 cm, 38.1 cm, and 86.4 cm, giving about 17%.
How to use it
- Choose your sex and unit system at the top.
- Enter your height, neck, and waist. Women also enter hips.
- Read your estimated body fat percentage and its category.
- Switch units at any time. The calculator reconverts your figures for you.
Limitations
This is an estimate, not a diagnosis. The circumference method cannot tell exactly where fat sits, it assumes an average build, and it can read high or low for very muscular or very lean people. It is not validated for children, and pregnancy changes the measurements it relies on. Measure carefully, compare results over time rather than fixating on a single reading, and speak with a clinician before drawing any conclusion about your health.
Frequently asked questions
How accurate is the Navy body fat method?
It is a reasonable estimate for most people, usually within a few points of a clinical measurement, but it is not a precise reading. It relies on tape measurements and a population formula, so a wrong tape position or an unusual build can shift the result. Treat it as a quick screening number you can track over time, not a lab value. For a precise figure, a DEXA scan or hydrostatic weighing is the gold standard.
Where exactly do I measure?
Measure the neck just below the larynx, with the tape sloping slightly down to the front. For men, measure the waist horizontally at the navel. For women, measure the waist at its narrowest point and the hips at their widest point. Keep the tape snug but do not compress the skin, breathe normally, and avoid measuring right after a meal. Taking each measurement twice and averaging reduces error.
Why does the women's formula need a hip measurement?
Body fat is distributed differently by sex, so the two equations use different inputs to fit their populations. The men's formula uses neck and waist. The women's formula adds the hip circumference because hip girth carries more information about fat distribution in women, which improves the estimate. That is why the hip field only appears when you select female.
What is a healthy body fat percentage?
It depends on sex and goals. Using the American Council on Exercise ranges, men are typically described as essential fat at 2 to 5 percent, athletes 6 to 13, fitness 14 to 17, average 18 to 24, and above that obese. For women the same labels sit higher: essential 10 to 13, athletes 14 to 20, fitness 21 to 24, average 25 to 31, and above that obese. Women carry more essential fat for normal physiology, so their healthy ranges are higher than men's.
Why did the calculator refuse to give a number?
The formula uses the difference between your waist and neck, and that difference has to be a real positive figure. If the waist is not larger than the neck, or a value was mistyped, the math has no valid result and the tool shows the empty state instead of an invented number. Re-check that your waist measurement is bigger than your neck and that every field is in the same unit.