This body fat calculator estimates your body fat percentage using the U.S. Navy circumference method — the same tape-measure technique the Navy uses to assess its personnel. Instead of expensive scans, it needs only your height plus neck and waist measurements (and hips for women), making it one of the most practical ways to track body composition at home.
Body fat percentage tells you something the bathroom scale cannot: how much of your weight is fat versus lean tissue like muscle, bone, and water. Two people can weigh exactly the same yet look and perform completely differently. Enter your measurements below to get your body fat percentage, category, fat mass, and lean mass.
How the U.S. Navy Method Works
Developed at the Naval Health Research Center by Hodgdon and Beckett in 1984, the method predicts body density from circumference measurements, then converts it to body fat percentage. With measurements in centimeters:
- Men: BF% = 495 ÷ (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450
- Women: BF% = 495 ÷ (1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.22100 × log₁₀(height)) − 450
Measure your neck just below the larynx, your waist at the navel (men) or the narrowest point (women), and hips at the widest point. Keep the tape snug but not compressing the skin, and take each measurement two or three times. Studies find the method accurate to within roughly 3–4 percentage points of laboratory techniques for most people.
Body Fat Percentage Categories (ACE Chart)
The American Council on Exercise classifies body fat percentage as follows:
- Essential fat: 2–5% (men), 10–13% (women) — the minimum needed for basic physiological function
- Athletes: 6–13% (men), 14–20% (women)
- Fitness: 14–17% (men), 21–24% (women)
- Average: 18–24% (men), 25–31% (women)
- Obese: 25%+ (men), 32%+ (women)
Women carry more essential fat than men because of reproductive and hormonal needs — dropping near or below the essential range can disrupt hormone levels for either sex. For general health, most men do well between 10% and 20% and most women between 18% and 28%. Visible abdominal definition typically appears around 10–12% for men and 16–19% for women.
Example: Male, 5'10", Neck 15", Waist 34"
Convert to centimeters: height 70 in × 2.54 = 177.8 cm, neck 15 in × 2.54 = 38.1 cm, waist 34 in × 2.54 = 86.4 cm.
waist − neck = 86.4 − 38.1 = 48.3 cm
BF% = 495 ÷ (1.0324 − 0.19077 × log₁₀(48.3) + 0.15456 × log₁₀(177.8)) − 450 = 495 ÷ (1.0324 − 0.3212 + 0.3477) − 450 = 495 ÷ 1.0590 − 450 ≈ 17.4%
That lands at the top of the ACE "Fitness" range for men. If he weighs 165 lbs, his fat mass is 165 × 0.174 ≈ 28.8 lbs and his lean mass is about 136.2 lbs — useful numbers for setting protein targets and tracking whether weight loss is coming from fat or muscle.
Frequently Asked Questions
What is a healthy body fat percentage?
For general health, roughly 10–20% body fat for men and 18–28% for women is a sensible target, based on ACE categories. Athletes often sit lower — 6–13% for men and 14–20% for women. Falling below essential fat levels (2–5% men, 10–13% women) is dangerous and disrupts hormone function.
How accurate is the Navy body fat method?
Validation studies show the Navy circumference method is typically within 3–4 percentage points of laboratory methods like hydrostatic weighing or DEXA scans for most body types. Accuracy drops for very muscular or very lean individuals. Consistent technique matters most — measure at the same spots, at the same time of day.
Where exactly do I measure my waist, neck, and hips?
Measure the neck just below the larynx (Adam's apple) with the tape sloping slightly downward in front. Men measure the waist horizontally at the navel; women measure at the narrowest point. Women also measure hips at the widest point. Keep the tape level and snug without compressing the skin.
Why do women need to enter a hip measurement?
Women store proportionally more fat in the hips and thighs, so the female Navy formula adds hip circumference to capture that pattern. The male formula relies on waist minus neck because men store fat predominantly in the abdomen. Using the wrong formula for your body would skew the estimate significantly.
What is the difference between fat mass and lean mass?
Fat mass is your total weight multiplied by your body fat percentage; lean mass is everything else — muscle, bone, organs, and water. Tracking both shows whether a diet is working: ideally fat mass falls while lean mass holds steady, which requires adequate protein and resistance training.