Body Fat Calculator
Estimate your body fat percentage from height, neck, waist and hip measurements using the US Navy circumference method. Metric and imperial supported.
Enter your measurements and press Calculate body fat.
What the body fat calculator does
This calculator estimates body fat percentage from a few tape measurements using the US Navy circumference method. You enter your height, neck and waist, and if you are a woman, your hip measurement too. The tool places those numbers into a logarithmic regression equation and returns one percentage, along with the reference band that percentage falls into.
The method needs nothing more than a flexible tape measure. It does not measure fat directly. It relies on the fact that body shape changes with body fat in a fairly consistent way across many people. That makes it useful for watching your own trend over weeks, and less useful for judging a single reading in isolation.
How to use it
- Choose Metric (cm) or Imperial (in). Either works, because the tool converts inches to centimetres before it calculates.
- Select your sex. The male and female formulas use different measurements.
- Measure your height without shoes, standing straight.
- Measure your neck just below the larynx, with the tape sloping slightly downward toward the front.
- Measure your waist at the navel. Breathe out normally, and keep the tape level and snug without pressing into the skin.
- If you selected female, measure your hip at the widest point of the buttocks.
- Press Calculate body fat. If the numbers cannot produce a valid estimate, a message explains which relationship failed.
Worked example
Take a man who is 178 cm tall, with a 38 cm neck and an 84 cm waist. The waist minus neck is 46 cm, and the formula works out as follows:
- 86.010 × log10(46) = 142.99
- 70.041 × log10(178) = 157.62
- 142.99 − 157.62 + 36.76 = 22.1%
Under the reference bands for men, 22.1% falls in the Average range of 18 to 24%. If the waist were 90 cm instead, the waist minus neck becomes 52 cm and the estimate rises to about 26.7%, which is in the band starting at 25%. A change of six centimetres on the waist moves the result by more than four percentage points, so consistent measuring matters.
Tips and limits
- Measure at the same time of day, ideally in the morning before eating, and use the same tape each time.
- Take each measurement twice and use the average. If the two readings differ by more than about a centimetre, measure again.
- The result is an estimate. Athletes, people with a lot of muscle, and people whose fat is stored unusually can land in a band that does not match how they look or feel.
- The bands are reference ranges, not a diagnosis. When a precise figure matters, a clinician or certified assessor can use skinfold calipers or a DXA scan instead.
Body Fat Calculator – Frequently Asked Questions
Which measurements does the US Navy method need?
Men need height, neck and waist. Women also need hip. The neck is measured just below the larynx, the waist at the navel, and the hip at the widest part of the buttocks. Height is taken without shoes.
How accurate is a tape-measure body fat estimate?
It is a population-level estimate. Compared with laboratory methods such as DXA scans or hydrostatic weighing, an individual result can be several percentage points off. It is most useful for tracking your own trend with the same tape and the same routine each time.
Why must the waist be larger than the neck?
The formula takes the logarithm of waist minus neck for men, and of waist plus hip minus neck for women. A logarithm is undefined for zero or negative values, so the calculator rejects measurements that would produce one.
What do the body fat bands mean?
The bands are the reference ranges published by the American Council on Exercise. For men: 2 to 5% essential fat, 6 to 13% athlete, 14 to 17% fitness, 18 to 24% average, and 25% and above obese. For women: 10 to 13% essential fat, 14 to 20% athlete, 21 to 24% fitness, 25 to 31% average, and 32% and above obese.
Can I enter imperial measurements?
Yes. In imperial mode the values are read as inches and converted at 2.54 cm per inch before the formula runs. The result is the same as entering the equivalent centimetre values.