Body Fat Calculator: US Navy Method With a Tape Measure
Measure your waist, neck and height (plus hips for women) to estimate your body fat percentage with the US Navy formula and see which category you fall in.
Men: at the navel. Women: at the narrowest point.
Just below the Adam’s apple.
Short answer
The US Navy method estimates body fat from a few tape measurements and your height. Example with made-up numbers: a man 180 cm tall with an 85 cm waist and a 38 cm neck comes out at about 16.1% body fat, in the "fitness" band. A woman 165 cm tall with a 72 cm waist, 96 cm hips and a 33 cm neck comes out at about 25.9%, in the "average" band.
The formulas
The calculator uses the equations developed for the US Navy by Hodgdon & Beckett (1984, men) and Hodgdon & Beckett (1984, women), in centimetres. Each one predicts body density, which is then turned into a percentage with Siri's equation (495 ÷ density − 450):
- Men: body fat % = 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450
- Women: body fat % = 495 ÷ (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450
Small changes in the waist move the result quite a bit. For the example man (180 cm, 38 cm neck):
Waist | Body fat |
|---|---|
80 cm | 12.1% |
85 cm | 16.1% |
90 cm | 19.8% |
95 cm | 23.2% |
100 cm | 26.4% |
How to measure
The Navy reports define the sites like this:
- Neck: just below the larynx (Adam's apple), with the tape sloping slightly down towards the front.
- Waist, men: around the abdomen at the level of the navel.
- Waist, women: at the narrowest part of the abdomen, roughly halfway between the bottom of the breastbone and the navel.
- Hips, women: around the widest part of the hips and buttocks.
Stand relaxed, breathe out normally and don't pull your stomach in. Keep the tape snug on the skin without pressing in. Measure each site two or three times and use the average. For tracking, measure at the same time of day, ideally in the morning before eating.
Body fat categories
The result is placed in the categories published by the American Council on Exercise (ACE):
Category | Men | Women |
|---|---|---|
Essential fat | 2 to 5% | 10 to 13% |
Athletes | 6 to 13% | 14 to 20% |
Fitness | 14 to 17% | 21 to 24% |
Average | 18 to 24% | 25 to 31% |
Obese | 25% or more | 32% or more |
Essential fat is the minimum the body needs to work normally. It is a floor, not a goal.
How accurate is it?
When the men's equation was tested on a separate group of 100 Navy men against underwater weighing, the correlation was 0.90 and the standard error was 2.7 percentage points. The women's equation was less precise: when it was tested on two other groups of women, the standard error was about 4 percentage points. In plain terms, a reading of 16% could easily be 13% or 19%.
Tape methods also assume an average fat distribution. If you carry most of your fat on your hips and thighs, or you have a very thick neck from training, the estimate can be off in one direction. The method is most useful for tracking change: same tape, same person measuring, same time of day, every few weeks.
The numbers on this page are general information. Body fat alone doesn't tell you whether you are healthy. If you are worried about your weight or your health, talk to a doctor.
Frequently asked questions
How accurate is the Navy body fat calculator?
In the original Navy validation, the men's equation had a standard error of about 2.7 percentage points against underwater weighing, and the women's about 4. Use it to track trends, not as an exact number.
How do I measure my waist for body fat?
Men measure around the navel. Women measure at the narrowest part of the abdomen, about halfway between the breastbone and the navel. Stand relaxed and don't pull your stomach in.
What is a healthy body fat percentage?
In the ACE chart, the "fitness" band is 14 to 17% for men and 21 to 24% for women, and "average" is 18 to 24% and 25 to 31%. What is right for you also depends on age, health and goals.
Why do women have a higher body fat percentage than men?
Women carry more essential fat, which is why every category in the chart sits higher for women, starting at 10 to 13% essential fat compared with 2 to 5% for men.
Is the Navy method better than a smart scale?
Both are estimates. The Navy equations miss by about 3 to 4 points on average, and scales can be off too. The tape is cheap and repeatable; whichever you use, stick to one method and compare readings taken under the same conditions.
This is general information, not medical advice. Talk to a professional about your own situation.