Body fat calculator
Estimate your body fat percentage from a few tape measurements, using the US Navy method. Unlike BMI, it separates fat from lean tissue, although it is still an estimate with a real margin of error.
Uses a standard published formula, explained below. The result is an estimate, not medical advice, and its limits are explained further down the page.
Measurements
Estimated body fat
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Fat mass
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Lean mass
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Category
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Show the working
—An estimate with a typical error of three to four percentage points. The US Navy method infers body fat from circumferences, so it cannot see your actual composition and performs worst at the extremes and for people whose fat distribution is unusual. A DEXA scan is the accepted reference standard. Do not use this figure to set aggressive goals, and speak to a doctor or dietitian before making significant changes.
How to measure yourself correctly
The result is only as accurate as your measurements, and measuring mistakes are the biggest source of error. Being one centimeter out on your waist can change the result by about a full percentage point.
- Neck: measure just below the Adam's apple, with the tape sloping slightly down at the front. Do not tense your neck.
- Waist: men should measure at the navel, and women at the narrowest point of the waist. Measure after breathing out normally, without pulling your stomach in.
- Hips: women only. Measure around the widest part of the buttocks, with your feet together.
Keep the tape snug without pressing into the skin, and keep it level all the way round. Measure at the same time of day each time; first thing in the morning, before eating, gives the most consistent results.
How the US Navy method works
The formula uses logarithms of your measurements, which is why it looks unfamiliar. For men, it is based on the difference between waist and neck size, adjusted for height. For women, hip size is also included, because women store fat differently. The method was developed by the US Naval Health Research Center as a practical alternative to underwater weighing.
It is important to understand that the tape does not measure fat directly. It measures body sizes that tend to go with certain levels of body fat in the people the formula was tested on, and estimates your body fat from those.
Healthy body fat ranges
Women need considerably more essential fat than men for hormonal and reproductive health, so the healthy ranges are different.
For men, the approximate ranges are 2% to 5% essential fat, 6% to 13% athletic, 14% to 17% fit, 18% to 24% average and 25% or more above the healthy range. For women, each range is about ten points higher: 10% to 13% essential, 14% to 20% athletic, 21% to 24% fit, 25% to 31% average and 32% or more above the healthy range.
Very low body fat is not a goal to aim for. Getting close to essential fat levels can disrupt hormones and the immune system, and in women it can stop periods. The lean end of these ranges is not healthier than the middle.
When this method is less accurate
The method assumes a typical link between body size and body fat, so it is less reliable for people with an unusual build. Very muscular people with thick necks tend to get a result that is too low. So do people who carry most of their weight on their arms and legs rather than their middle, because the tape never measures it. Accuracy is also lower at very low and very high body fat levels.
The method is more useful for tracking change over time than for a single reading. Because the error tends to stay the same for the same person, a steady downward trend over several months is meaningful even if the exact figure is not.
Frequently asked questions
What is a healthy body fat percentage?
Roughly 14% to 24% for men and 21% to 31% for women covers the fit and average ranges. Women need more essential fat than men for hormonal and reproductive health, so the ranges for men and women cannot be compared directly.
How accurate is the US Navy body fat method?
For people of average build, it is usually within three to four percentage points of more precise methods. It is less reliable for very muscular people, at very high or very low body fat, and for people with an unusual fat distribution.
Is body fat percentage better than BMI?
It tells you more, because it separates fat from muscle and other lean tissue. It is also harder to measure accurately, since a tape measurement has more room for error than the height and weight used for BMI.
What is the most accurate way to measure body fat?
A DEXA scan is the usual reference standard, with underwater weighing and air displacement close behind. All of them need clinic equipment. Home body fat scales are much less reliable, because their readings change with how much water you have drunk.
Can body fat be too low?
Yes. Body fat close to essential levels can disrupt hormones, the immune system and periods, and it is linked with weaker bones. Being leaner is not automatically healthier.
How fast can body fat change?
Slowly. Losing more than about half a percentage point a month while keeping your muscle is difficult. Bigger changes from one measurement to the next are usually caused by measuring error or changes in body water.