How to measure correctly
The measuring points decide the result. Just two centimeters of difference in your abdomen circumference shift the calculated body fat percentage noticeably. So stick closely to these steps:
- Timing: measure in the morning before breakfast. Over the course of the day, meals and fluids change your abdomen circumference.
- Preparation: measure on bare skin. Hold the tape horizontally, snug but not digging in. Do not pull your belly in and breathe out normally before reading the value.
- Neck (men and women): measure just below the larynx, with the tape sloping slightly downward toward the front.
- Abdomen (men): measure at navel height, in a relaxed posture.
- Waist (women): measure at the narrowest point of the torso, usually slightly above the navel.
- Hips (women): measure at the widest point over the buttocks.
- Double-check: measure each spot twice and take the average. For tracking progress, always use exactly the same spots.
The formula: US Navy method
The method comes from Hodgdon and Beckett (Naval Health Research Center, 1984). It first estimates body density (BD) from body circumferences and height. All values are entered in centimeters:
Men: BD = 1.0324 - 0.19077 × log10(abdomen - neck) + 0.15456 × log10(height)
Women: BD = 1.29579 - 0.35004 × log10(waist + hips - neck) + 0.22100 × log10(height)
Body fat percentage then follows from body density via the Siri formula: body fat % = 495 ÷ BD - 450. An example: a man who is 180 cm tall with a 38 cm neck circumference and a 90 cm abdomen circumference comes to a body density of about 1.0536 and thus around 19.8% body fat.
Classification: body fat percentage table according to ACE
The American Council on Exercise (ACE) divides body fat percentage in adults into these categories. Women naturally sit higher, because their bodies require more essential fat:
| Category | Women | Men |
|---|---|---|
| Essential fat | 10 to 13% | 2 to 5% |
| Athletes | 14 to 20% | 6 to 13% |
| Fitness | 21 to 24% | 14 to 17% |
| Average | 25 to 31% | 18 to 24% |
| Above average | 32% and up | 25% and up |
The "above average" category means: the value is above the average range. This is a classification for orientation, not a health assessment. What suits you personally also depends on your age and training level.
How accurate is the tape measure method?
In comparison studies, the circumference method typically deviates by 3 to 4 percentage points from reference methods such as DXA scans. For very muscular people it often overestimates body fat percentage, and for severely overweight people it also becomes less reliable. So take the result as a guide, not as a lab value. In practice, the trend matters most: if you measure every few weeks under the same conditions, the development reliably shows you the direction, even if the absolute value may be off by a few points.
Body fat instead of BMI: when body fat percentage tells you more
The BMI only relates weight to height and cannot distinguish between muscle and fat mass. Body fat percentage can: a muscular person with a BMI of 27 can have a perfectly unremarkable body fat percentage. If you prefer something simpler, the BMI calculator also includes the waist-to-height check as a quick indicator of belly fat. Body fat percentage has another practical use: with it, your basal metabolic rate can be estimated more accurately using the Katch-McArdle formula, because it works with fat-free mass instead of total weight. You can try that out directly in our BMR calculator. And if you would like professional support, a qualified nutrition coach can guide you along the way.