Body Fat Calculator

How to calculate body fat percentage

This body fat calculator and body fat estimator computes your body fat percentage, fat mass, and lean body mass using two established circumference and anthropometric formulas: the U.S. Navy body fat method and the BMI-based prediction method. You can enter measurements in either US units (feet, inches, and pounds) or metric units (centimeters and kilograms).

1. U.S. Navy body fat calculator formula (Hodgdon & Beckett)

Developed by J.A. Hodgdon and M.B. Beckett at the Naval Health Research Center in 1984, the U.S. Navy circumference method estimates body density from height and tape-measure circumferences (in centimeters) and converts density to body fat percentage using the Siri equation:

• Men: Body Fat % = 495 ÷ (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450
• Women: Body Fat % = 495 ÷ (1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.22100 × log₁₀(height)) − 450

When you enter feet and inches in US mode, the calculator converts each measurement to centimeters (1 inch = 2.54 cm) before applying the equation above. Once body fat percentage is known:

• Body Fat Mass = Weight × (Body Fat % ÷ 100)
• Lean Body Mass = Weight − Body Fat Mass

2. BMI body fat percentage formula (Deurenberg et al.)

As a secondary comparison, the calculator estimates body fat from your Body Mass Index (BMI = weight in kg ÷ height in m²) and age using the prediction equations published by Deurenberg, Weststrate, and Seidell (1991). While the original 1991 study derived its child equation in subjects aged 15 and younger, this calculator applies the youth formula through age 17 and switches to the adult formula at age 18:

• Adult men (age 18+): Body Fat % = 1.20 × BMI + 0.23 × Age − 16.2
• Adult women (age 18+): Body Fat % = 1.20 × BMI + 0.23 × Age − 5.4
• Boys (ages 2–17): Body Fat % = 1.51 × BMI − 0.70 × Age − 2.2
• Girls (ages 2–17): Body Fat % = 1.51 × BMI − 0.70 × Age + 1.4

What is a healthy body fat percentage?

Essential fat is the minimum amount of fat required for normal physiological and hormonal function—roughly 2–5% in men and 10–13% in women because of sex-specific reproductive and hormonal tissue. The American Council on Exercise (ACE) groups body fat percentage into five reference ranges, and fitness assessment tables commonly attributed to Jackson & Pollock provide age-based ideal body fat targets for adults aged 20 to 55:

What the result includes

• Body fat (U.S. Navy method) and its ACE body fat category on a visual scale.
• Body fat mass and lean body mass shown in both pounds and kilograms.
• Ideal body fat for given age (Jackson & Pollock) and the body fat to lose or gain to reach ideal (for ages 20 to 55, linearly interpolated between 5-year benchmarks).
• Body fat (BMI method) for side-by-side comparison with the circumference method.

Important caveats

Tape-measure and BMI formulas provide convenient population estimates, typically within 3–4 percentage points of laboratory methods such as dual-energy X-ray absorptiometry (DEXA) or hydrostatic weighing. Results are for general educational and fitness tracking purposes only and are not a substitute for professional medical evaluation.

Frequently asked questions

How should I measure my neck, waist, and hips for the Navy body fat calculator?

Measure against bare skin to the nearest 1⁄4 inch (0.5 cm) without pulling the tape tight. Measure your neck just below the larynx (Adam's apple) with the tape sloping slightly downward to the front. Measure your waist horizontally at the navel for men, or at the narrowest part of the torso for women, after a normal exhale. For women, measure your hips horizontally around the widest part of the buttocks.

Why do the U.S. Navy method and the BMI method give different numbers?

The BMI method only uses height, weight, age, and sex, so it cannot distinguish between muscle mass and fat mass—a muscular athlete often has a high BMI and an overestimated BMI body fat percentage. The U.S. Navy method accounts for waist, neck, and hip circumferences, which better reflects abdominal fat versus lean frame size.

Why is essential body fat higher for women than for men?

Women require additional essential fat in breast, pelvic, hip, and thigh tissues to support normal endocrine and reproductive function. Dropping into or below the essential fat range (under 10–13% for women or 2–5% for men) can impair hormone production, bone density, and organ health.