Body Fat Percentage Calculator

How the US Navy method works

You enter four measurements (men) or five (women), and the formula returns your body fat percentage. It’s the most accurate body composition estimate you can get without specialised equipment.

Men: %BF = 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76

Women: %BF = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387

All measurements in centimetres. Hodgdon and Beckett published this in 1984 after validating it on 1605 US Navy personnel against hydrostatic weighing — the laboratory gold standard at the time.

How to measure correctly

The accuracy of the formula depends entirely on the quality of your measurements. Use a flexible non-stretch tape measure.

• Neck: just below the larynx, with the tape sloping slightly downward.
• Waist: at the level of your navel for men; at the narrowest point between ribs and hips for women.
• Hips (women only): at the widest point of the buttocks.
• Height: barefoot, against a wall.

Measure on bare skin or thin clothing. Keep the tape snug but don’t compress soft tissue. Take each measurement twice and use the average.

Reference categories (ACE 2018)

The athletic ranges are common targets for serious recreational lifters and runners. Going below the lower bound consistently — for women below 14%, men below 6% — risks endocrine disruption, sleep loss, and immune impairment. It’s not a goal worth pursuing for most people.

Pair this with our other tools

Body fat percentage is one input. For a complete metabolic snapshot:

• BMI calculator — population-level screening, fast and crude.
• Waist-to-hip ratio — independent cardiovascular risk signal.
• BMR & TDEE calculator — daily energy needs based on Mifflin-St Jeor.
• Macro calculator — protein/carb/fat split aligned with ISSN 2017.

When the Navy method falls short

• Very lean athletes (men <8%, women <16%) — the regression underpredicts fat slightly.
• Severe obesity — the equation extrapolates beyond its validation range.
• Pregnancy — uterine and breast changes confound the waist measurement.
• Postpartum — the abdominal muscles may not have fully reverted; expect noisy results for 6–12 months.

In those situations, prefer DEXA, BodPod, or BIA at a clinical lab if precise values matter.

Privacy

All calculation happens in your browser. We never see, log, or store your measurements. Anonymous category-bucket events go to our privacy-first analytics — no personally identifiable information is collected.