Body Fat Categories (ACE Guidelines)
| Category | Men | Women |
|---|---|---|
| Essential Fat | 2-5% | 10-13% |
| Athletes | 6-13% | 14-20% |
| Fitness | 14-17% | 21-24% |
| Average | 18-24% | 25-31% |
| Obese | 25%+ | 32%+ |
These bands come from the American Council on Exercise. Essential fat is the minimum the body needs for hormones, nerves and organs, and women need more of it than men. Going below it is dangerous.
The US Navy formula
Hodgdon and Beckett at the Naval Health Research Center built these equations in 1984 from measurements of Navy men and women checked against underwater weighing. The metric form is:
Men: BF% = 495 / (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450
Women: BF% = 495 / (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450
All measurements in centimeters.
Worked example (woman). Height 165 cm, neck 33 cm, waist 75 cm, hips 100 cm. Waist + hip − neck = 142, and log10(142) = 2.1523. log10(165) = 2.2175. The bracket is 1.29579 − 0.35004 × 2.1523 + 0.221 × 2.2175 = 1.0325. Then 495 ÷ 1.0325 − 450 = 29.4%, in the ACE average band for women.
The BMI method
Deurenberg and colleagues (1991) estimated body fat from BMI, age and sex: BF% = 1.2 × BMI + 0.23 × age − 10.8 × sex − 5.4, where sex is 1 for men and 0 for women. It needs no tape measure but cannot tell muscle from fat, so it overestimates body fat in muscular people. When the two methods disagree by more than a few points, the tape method is usually closer for fit people.
How to measure
Use a flexible tape, stand relaxed and breathe out normally. Neck: just below the larynx, tape sloping slightly down to the front. Waist: men at the navel, women at the narrowest point of the waist. Hips (women): at the widest part of the buttocks. Measure two or three times and use the average; for a man of average build, one centimeter on the waist moves the result by about three quarters of a percentage point.
Accuracy and limits
Note: Body fat calculators provide estimates only. DEXA scans and hydrostatic weighing are the most accurate clinical methods. Consult a healthcare professional for precise measurement. Circumference equations can be off by several percentage points for an individual, and a 2022 study of fit US Marines found an abdominal circumference method underestimated men's body fat by about 2.5 points on average and overestimated women's by 1 to 2 points compared with DXA, with individual errors of about 4 points either way. Use the result to track change over time with the same tape and technique, not as a single verdict.