A More Useful Number Than Weight Alone
Body fat percentage says what your weight is made of, which the number on a scale cannot. Two people at the same height and weight can differ by fifteen points of body fat, and everything from how they look to their health risk differs with it. It is also why weight can stay flat during months of training that clearly changed the body underneath.
This calculator estimates body fat two ways: the US Navy method, which uses tape measurements, and a BMI-derived estimate that needs only height, weight, age and sex.
How to Measure and Calculate
The Navy method is the more useful of the two, and its accuracy is decided almost entirely by how you hold the tape.
- Choose the method. Use the Navy method if you have a tape measure; the BMI-based estimate is a fallback when you do not.
- Measure your neck just below the larynx, with the tape sloping slightly downward at the front.
- Measure your waist at the navel for men, and at the narrowest point for women. Breathe out normally and measure then, not while holding your stomach in.
- For women, also measure the hips at their widest point.
- Keep the tape snug against the skin but not compressing it, and level all the way round. A tape that dips at the back is the most common source of error.
- Enter your measurements with height, age and sex, and compare the result with the category table below.
How the Two Methods Differ
The Navy method uses circumferences, so it responds to where your body actually carries fat and tracks changes over time reasonably well. Against a DXA scan it is typically within three to four percentage points, which is good enough to follow a trend but not precise enough to argue about a single point.
The BMI-derived estimate is less reliable because BMI cannot distinguish muscle from fat. It will overestimate body fat in muscular people and underestimate it in someone with low muscle mass at a normal weight. Use it when you have no tape, and treat any result close to a category boundary as unresolved.
Body Fat Percentage Categories
Commonly cited ranges from the American Council on Exercise. Healthy ranges differ substantially by sex because essential fat does.
| Category | Women | Men |
|---|---|---|
| Essential fat | 10–13% | 2–5% |
| Athletes | 14–20% | 6–13% |
| Fitness | 21–24% | 14–17% |
| Average | 25–31% | 18–24% |
| Obese | 32% and above | 25% and above |
These bands are population guidance, not diagnostic thresholds, and they shift with age, an older adult in good health commonly sits above the fitness range. Being below essential fat is not an achievement; it is associated with hormonal and immune problems.
Measuring Consistently Matters More Than Measuring Precisely
Because every field method carries a few points of error, a single reading tells you less than a series does. Measure at the same time of day, in the same conditions, ideally in the morning before eating, and compare readings a few weeks apart rather than day to day. A consistent method with a known bias is more useful than an accurate one you apply differently each time.
This calculator provides general-interest estimates and is not medical advice or a diagnosis. Body composition interacts with age, medication, pregnancy and a range of conditions, and a clinician with access to proper measurement equipment is the right source for anything you plan to act on.