How to take your measurements
- Use a flexible, non-stretch tape measure and measure against bare skin.
- Neck: just below the larynx (Adam’s apple), with the tape sloping slightly down at the front.
- Waist (men): horizontally at the level of the navel.
- Waist (women): at the narrowest point of the natural waist.
- Hip (women): at the widest point of the buttocks.
- Stand relaxed, breathe out normally and keep the tape snug but not compressing the skin.
- Take each measurement twice and use the average.
The U.S. Navy formula
If you enter your age, FitNumbra also shows a BMI-based estimate (Deurenberg et al., 1991) for comparison. The two methods often differ by a few percentage points — neither is a precise measurement.
Body-fat categories
These ranges are from the American Council on Exercise (ACE) and are widely used in fitness settings:
| Category | Women | Men |
|---|---|---|
| Essential fat | 10–13% | 2–5% |
| Athletes | 14–20% | 6–13% |
| Fitness | 21–24% | 14–17% |
| Average | 25–31% | 18–24% |
| Obesity range | 32% and above | 25% and above |
How accurate is this?
Tape-measure methods are convenient but approximate. Studies comparing the Navy method with laboratory methods typically find errors of several percentage points for individuals, and results can be less accurate at very high or very low body fat. DXA scans and other clinical methods are more precise but still have some error.
The most useful way to use this calculator is to track the trend over weeks and months with consistent measuring, rather than focusing on one reading.
Frequently asked questions
What is a healthy body fat percentage?
Ranges vary by source, age and sex. On the ACE chart, the “fitness” and “average” categories (roughly 21–31% for women and 14–24% for men) are common for healthy adults.
Is the U.S. Navy method accurate?
It is a reasonable estimate for many people but can be off by several percentage points for an individual. It is not equivalent to a clinical measurement such as DXA.
Why do women need a hip measurement?
Women typically store more fat around the hips, so the women’s version of the formula includes hip circumference to improve the estimate.
Why is my body-fat estimate different from my smart scale?
Smart scales use bioelectrical impedance, which is affected by hydration, food and exercise. Different methods measure different things, so results rarely match exactly.
Methods and sources
- Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy men and women from body circumferences and height. Naval Health Research Center, 1984.
- Deurenberg P, Weststrate JA, Seidell JC. Body mass index as a measure of body fatness: age- and sex-specific prediction formulas. Br J Nutr. 1991;65(2):105–114.
- American Council on Exercise (ACE) — body-fat percentage categories
Content reviewed: by the FitNumbra editorial team.