Know your body
Body fat calculator
All you need is a tape measure. The U.S. Navy method estimates body fat from neck, waist (and hips, for women) and height. It is not a lab test, but measured carefully and repeated under the same conditions it is excellent for tracking change.
Your numbers
Just below the larynx
Level with the navel
Your body fat appears here
Enter height, neck and waist. Measure in the morning, tape level and snug.
How it’s calculated
The formula
Hodgdon & Beckett (1984), metric form. Men: 495 ÷ (1.0324 − 0.19077·log₁₀(waist − neck) + 0.15456·log₁₀(height)) − 450. Women: 495 ÷ (1.29579 − 0.35004·log₁₀(waist + hip − neck) + 0.22100·log₁₀(height)) − 450.
How to measure
- Neck: just below the larynx, tape sloping slightly down to the front.
- Waist (men): horizontally at the navel, relaxed, after a normal exhale.
- Waist (women): at the narrowest point.
- Hips (women): at the widest point of the buttocks. Measure first thing in the morning, twice, and use the average.
Accuracy
Against DEXA and hydrostatic weighing, the Navy method is typically within ±3–4 percentage points for most people, with larger errors at the extremes. Its strength is consistency: the same person measured the same way gives a reliable trend.
Full sources and limitations are on the methodology page. Estimates are for healthy adults and are not medical advice.
Questions
How accurate is the Navy body fat method?
Usually within 3–4 percentage points of a DEXA scan. That is similar to consumer bioimpedance scales, and more consistent over time when you measure carefully.
Why does it give a different answer from my smart scale?
Bioimpedance scales estimate body fat from how electricity passes through you, which swings with hydration. Neither is “the truth” — pick one method and track the trend.
Is the BMI-based estimate useful?
Only as a rough comparison. It cannot tell muscle from fat, so it overestimates body fat in anyone who lifts.