OnSumoTools

Body Fat Percentage Calculator

Estimate body fat using Navy circumference and BMI-based methods. See lean mass, fat mass, and ACE fitness classification.

Unit system

Body Fat % (Navy)

17.8%

Average

Body Fat % (BMI-based)

20.1%

Deurenberg formula estimate

Body Composition

Lean mass

61.7 kg

Fat mass

13.4 kg

Total weight

75 kg

ACE Classification (Male)

CategoryRange
Essential2–5%
Athletes6–13%
Fitness14–17%
Average18–24%
Obese25%+

Navy circumference method has a 3–4% error margin compared to DEXA scans. Results vary with measurement technique and individual body proportions. This is not medical advice.

How does the Body Fat Calculator work step by step?

The tool estimates body fat percentage using two independent methods. The Navy method uses circumference measurements: for men, BF% = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76; for women, BF% = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387 (all in inches). The Deurenberg BMI-based formula provides a secondary estimate: BF% = 1.20 × BMI + 0.23 × age − 16.2 (men) or − 5.4 (women). Lean mass equals total weight minus fat mass. The ACE fitness classification rates your result against population standards: Essential fat (2–5% men, 10–13% women), Athletes (6–13% / 14–20%), Fitness (14–17% / 21–24%), Average (18–24% / 25–31%), Obese (25%+ / 32%+).

What does a typical Body Fat Calculator result look like?

A 30-year-old man, 175 cm tall with a 37 cm neck and 85 cm waist, converts to 68.9 in height, 14.6 in neck, and 33.5 in waist. Navy BF% = 86.010 × log10(33.5 − 14.6) − 70.041 × log10(68.9) + 36.76 ≈ 19.2%. At 75 kg that gives 14.4 kg fat mass and 60.6 kg lean mass, placing him in the Average ACE category.

Frequently asked questions

  • What is a healthy body fat percentage?

    For men, 10% to 20% is generally considered healthy. For women, 18% to 28% is healthy. Health risk increases at the high and low extremes. Below essential fat levels, you risk hormonal and immune system problems. Above 25% for men or 32% for women, you have higher risk of metabolic disease.

  • How accurate are body fat calculators?

    Most online calculators provide estimates that can be off by 3% to 5%. They are useful for tracking trends over time but not for precise measurement. For more accuracy, consider DEXA scans, bod pods, or hydrostatic weighing. Use the same calculator and method consistently so changes reflect real progress.

  • How can I reduce body fat percentage?

    To reduce body fat, you need to lose fat mass while maintaining or building lean mass. That usually means eating in a calorie deficit, getting enough protein to preserve muscle, and including resistance training. A slow fat loss rate of 0.5% to 1% body fat per month is sustainable and preserves muscle better than rapid weight loss.

  • Is body fat percentage more important than BMI?

    Body fat percentage gives a better picture of body composition than BMI because it separates fat from muscle. BMI can misclassify muscular people as overweight and miss high body fat in people with low muscle mass. If you can only track one, body fat percentage is more useful. But both together give the most complete picture.

  • Why do women have higher body fat than men?

    Women naturally carry more essential fat due to reproductive function and hormone regulation. Essential fat for women is 10% to 13% compared to 2% to 5% for men. This difference is biological and normal. Healthy body fat ranges for women are about 8 to 10 percentage points higher than for men at every fitness level.

  • Can you have low BMI but high body fat?

    Yes. This is called normal-weight obesity or skinny fat. It happens when someone has low muscle mass and high body fat but stays within the normal BMI range. Body fat percentage and waist circumference are better indicators of health risk than BMI alone for people in this situation.

Related tools

Estimate body fat with a tape measure

Body fat percentage is the share of your weight that's fat. It says more about your composition than the scale or BMI. Lab methods like DEXA scans are accurate and cost money. This calculator gives you a reasonable estimate from simple measurements.

It supports the U.S. Navy method, which uses height, neck and waist (and hip for women), and a BMI-based method that uses age, sex, height and weight. Then it splits your weight into fat mass and lean mass.

Taking good measurements

Use a soft tape. Measure the neck just below the larynx. Measure the waist at the navel for men, at the narrowest point for women. Keep the tape snug but not pressing into skin. Take each measurement twice and use the average.

A one-centimeter error can move the result by a point or more. Measure in the morning, before eating, and on the same day each time you repeat it.

What counts as healthy

The ACE fitness categories are a common reference. For men, roughly 2 to 5 percent is essential fat, 6 to 13 is athletic, 14 to 17 is fit, 18 to 24 is average and 25 or more is obese. For women the ranges sit higher: 10 to 13 essential, 14 to 20 athletic, 21 to 24 fit, 25 to 31 average, 32 or more obese.

Women carry more essential fat than men. It supports hormones and reproduction, which is why healthy ranges differ. Going below the essential range is dangerous, not a goal.

How accurate is it?

Expect an error of several percentage points. Tape and formula methods work best for tracking your own trend over weeks, not for pinning down a precise value. Use the same method every time so changes mean something.

Body fat versus BMI

BMI can't separate muscle from fat. Someone can have a normal BMI and still carry a high share of body fat with little muscle. Doctors sometimes call that being skinny fat. The opposite happens too, with a muscular person who looks overweight on BMI.

If your measurements are available, body fat is the more informative number.

Lowering it

Eat a modest calorie deficit, get enough protein, lift weights and sleep properly. That combination loses fat and holds on to muscle. Aggressive cuts burn muscle too. You can't pick where fat comes off, so spot-reduction exercises don't work.

This tool offers general information, not medical advice. Your measurements stay in your browser.