A worked example
A woman 170 cm tall with a 33 cm neck, 76 cm waist and 100 cm hips comes out at about 29% body fat, in the ACE “Average” band. At 68 kg that’s 19.7 kg of fat.
Where to measure
Stand relaxed and keep the tape level, snug against the skin without pressing in. Measure your neck just below the larynx (the Adam’s apple). For the male formula, measure your waist around the navel. For the female formula, measure the waist at its narrowest and the hips at their widest. Breathe out normally before each waist reading.
How good is a tape-measure estimate?
This is the US Navy circumference method, with the equations published in the NOAA Corps directive. Against lab methods it usually lands within about 3 to 4 percentage points, which is similar to most home scales that claim to measure body fat.
Moving the tape a centimetre or two changes the answer, so the trend matters more than any single reading. Measure at the same spot, at the same time of day, and compare month to month.
The ACE categories
The American Council on Exercise groups body fat into five bands, and the category with your result comes from this table. They describe where people typically fall and aren’t medical cut-offs.
| 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%+ | 25%+ |
Questions people ask
Why are there separate male and female formulas?
Bodies store fat in different places on average, so the Navy fitted separate equations. The female one needs a hip measurement for that reason. Pick whichever matches your body better.
Is this better than BMI?
For most people, yes, because it uses where you carry size rather than weight alone. It’s still an estimate, and a DEXA scan is the lab standard if you need precision.
What’s the difference between fat mass and lean mass?
Fat mass is the estimated weight of body fat. Lean mass is everything else: muscle, bone, organs and water. The TDEE calculator can use lean mass through the Katch-McArdle formula.