Body Fat Calculator
Estimate your body fat percentage with the US Navy tape-measure method, see your ACE category, fat and lean mass, and compare with a BMI-based estimate.
Verified October 2026 · Sources: Hodgdon & Beckett 1984, Naval Health Research Center; American Council on Exercise (categories); Deurenberg et al., Br J Nutr 1991
Fat mass = weight × body fat % ; Lean mass = weight − fat mass
Deurenberg: 1.20 × BMI + 0.23 × age − 10.8 × sex (1 = male, 0 = female) − 5.4 = 22.9%
Weight at a target body fat (keeping your lean mass)
| Target body fat | Weight | Fat change |
|---|---|---|
| 10% (Athletes) | 72.6 kg | −9.4 kg |
| 14% (Fitness) | 76.0 kg | −6.0 kg |
| 18% (Average) | 79.7 kg | −2.3 kg |
| 22% (Average) | 83.8 kg | +1.8 kg |
| 25% (Obese) | 87.2 kg | +5.2 kg |
Assumes your lean mass (65.4 kg) stays the same. In practice, strength training and enough protein help preserve it while losing fat.
Your waist and body fat
| Waist | Estimated body fat |
|---|---|
| 82.5 cm | 14.4% |
| 85.0 cm | 16.5% |
| 87.5 cm | 18.4% |
| 90.0 cm (now) | 20.3% |
- Use a flexible, non-stretch tape; keep it level and snug without pressing into the skin.
- Measure on bare skin in the morning, before eating, after a normal breath out — don't suck in.
- Men: waist at the navel. Women: waist at the narrowest point, hips at the widest part of the buttocks.
- Neck: just below the Adam's apple, tape sloping slightly downward to the front.
- Take each measurement 2–3 times and use the average; small errors in the neck change the result a lot.
- →Re-measure every 2–4 weeks under the same conditions to track the trend.
- →Check your BMI and waist-to-height ratio for another view of weight-related risk.
- →Use the Calorie Calculator — add your body fat % to unlock the Katch-McArdle formula.
- →For a precise measurement, ask about a DEXA scan; for health concerns, talk to your doctor.
This tool is for informational purposes only. Always verify results with a qualified professional.
What is the Body Fat Calculator?
A body fat calculator estimates what percentage of your body weight is fat. Unlike BMI, which only compares weight with height, body fat percentage separates fat from lean mass (muscle, bone, organs and water), so it gives a better picture for muscular people and for anyone tracking changes in body composition. This calculator uses the US Navy circumference method — the tape-measure formula used for decades by the US military — and shows your result against the body fat categories published by the American Council on Exercise (ACE).
The US Navy method was developed by Hodgdon and Beckett at the Naval Health Research Center in 1984 from measurements of navy personnel compared with underwater weighing. With all measurements in inches, men use: body fat % = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76. Women add the hip measurement: body fat % = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387. Metric inputs are converted to inches before applying the formula, so metric and imperial give the same answer.
Worked example: a 35-year-old man, 178 cm tall and 82 kg, with a 38 cm neck and 90 cm waist (measured at the navel). Converted to inches that is a 70.1 in height, 15.0 in neck and 35.4 in waist, giving an estimated body fat of 20.3%. On the ACE scale for men that is in the 'average' range (18–24%). His fat mass is about 16.6 kg and lean mass about 65.4 kg. His BMI is 25.9, and the BMI-based Deurenberg formula estimates 22.9% — close to, but a little higher than, the tape-measure result.
ACE groups body fat for women as essential fat 10–13%, athletes 14–20%, fitness 21–24%, average 25–31% and obese 32% or more; for men essential fat 2–5%, athletes 6–13%, fitness 14–17%, average 18–24% and obese 25% or more. Women naturally carry more essential fat than men for reproductive health, which is why their ranges are higher. The ranges are not age-adjusted, and body fat tends to rise with age, so compare yourself mainly with your own previous results.
As a second opinion, the calculator shows the Deurenberg BMI-based estimate (British Journal of Nutrition, 1991): body fat % = 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4, where sex is 1 for men and 0 for women. Its authors noted it slightly overestimates body fat in people with obesity, and like BMI it cannot see muscle. Every home method has an error of several percentage points; DEXA scans or underwater weighing are more accurate. Use this estimate to track trends, not to diagnose anything.
How to Use This Calculator
- 1Choose metric or imperial units and select your sex — women also need a hip measurement.
- 2Enter your age, height and weight.
- 3Measure your neck just below the Adam's apple, sloping slightly down at the front.
- 4Measure your waist: men at the navel, women at the narrowest point; women also measure the hips at the widest point of the buttocks.
- 5Read your body fat %, ACE category, fat mass and lean mass, and compare with the BMI-based estimate.
- 6Use the target table to see the weight at a lower body fat if you keep your muscle, and re-measure every 2–4 weeks.