Body
Body fat percentage
The tape method beats anything BMI-derived, because circumferences actually respond to where fat sits. Measure the waist at the navel for men and at the narrowest point for women, neck just below the larynx.
Result
Breakdown
Worth knowing
- Accurate to roughly ±3% against hydrostatic weighing, and only if the tape is level and snug without compressing.
- Circumference methods assume typical fat distribution; they drift for very lean or very heavy bodies.
How this is calculated
Navy method: Hodgdon & Beckett (1984), estimating body density from log-transformed circumferences and converting via the Siri equation. Deurenberg (1991): 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4.
Common questions
How accurate is the tape method?
The US Navy formula lands within roughly ±3% of hydrostatic weighing when the measurements are taken properly. That is good enough to track change over months, and not good enough to argue about a single percentage point. Measure at the same time of day under the same conditions.
Where exactly do I put the tape?
Waist at the navel for men, at the narrowest point for women, and neck just below the larynx. Keep the tape level and snug without compressing the skin. Most of the disagreement people see between attempts comes from tape placement, not from real change.
Why do the two methods give me different numbers?
They use different inputs. The Navy method measures where your body actually carries fat; the Deurenberg estimate is derived from BMI, so it inherits BMI's blind spot and overestimates fat in muscular people. When you have a tape measure, trust the Navy figure.