Body Fat Percentage Calculator
Calculate your body fat %, fat mass, and lean mass using the Deurenberg and US Navy methods.
Example: A 35-year-old woman who is 5'6" (168 cm) and weighs 150 lb (68 kg) with a 32-inch waist has an estimated body fat percentage of around 28% using the US Navy method — within the "acceptable" range (25–31% for her age), with roughly 49 lb of fat mass and 101 lb of lean mass.
Uses the Deurenberg BMI-based formula and the US Navy circumference-based method side by side for cross-validation.
How this estimate is derived
- Model:
- Deurenberg BMI-based equation and the US Navy circumference method
- Primary reference:
- Deurenberg P et al., British Journal of Nutrition 1991;65:105-114; Hodgdon JA & Beckett MB, US Naval Health Research Center Report 84-29 (1984)
- Implementation last reviewed:
- 2026-08-29
- Purpose:
- Educational risk estimation only; not a clinical diagnosis.
How this is calculated
The Deurenberg formula estimates body fat percentage from your BMI, age, and sex — quick to compute from height and weight alone, but only an indirect proxy for actual body fat. The US Navy method instead uses waist, neck, and (for women) hip circumference, which more directly reflects your body shape and is generally the more accurate of the two.
Both differ from BMI, which uses height and weight only and cannot distinguish muscle from fat. See the BMI & Body Weight calculator for your BMI category, healthy weight range, and daily calorie needs.
Frequently asked questions
- What is body composition vs BMI?
- BMI uses only your height and weight — it cannot tell fat from muscle. Body composition measures the actual proportion of your body that is fat versus lean tissue (muscle, bone, organs, water), giving a more direct picture of your physical condition.
- Which method is more accurate?
- The US Navy circumference method is generally more accurate than the Deurenberg BMI-based formula, since it directly measures body shape rather than inferring it from height and weight alone. A DEXA scan, done in a clinical setting, is considered the gold standard.
- How do I measure my waist, neck, and hip?
- Use a flexible measuring tape. Waist: horizontal, at navel level. Neck: just below the larynx (Adam's apple), perpendicular to the neck's length. Hip: at the widest point around your buttocks (women only, for the US Navy method).
- What is essential fat?
- The minimum fat your body needs for normal physiological function — hormone production, organ protection, and more. Falling below essential fat levels is dangerous, not desirable.
- What is lean mass?
- Everything in your body that isn't fat: muscle, bone, organs, and water. It is calculated here as total weight minus fat mass.
- Is low body fat always better?
- No. Body fat below the essential range is dangerous. The "athlete" range is optimal for performance sports; the "fitness" range is a healthy general target for most active adults — lower isn't automatically healthier.
- How does age affect body fat?
- The Deurenberg formula includes age because body fat percentage tends to rise with age even at a stable BMI, largely due to gradual muscle loss (sarcopenia) that isn't reflected in weight or height alone.
- Can I use this in my own app?
- Yes — every calculator on Stupidly Clever has a matching REST API and MCP tool that runs the same underlying logic.