Body Fat Calculator
This free body fat calculator estimates your body fat percentage with the U.S. Navy tape-measure method — the same formula the U.S. military used to assess body composition. Grab a tape measure, enter your height, neck, waist (and hip) measurements, and get an instant estimate plus your category, from essential fat to obese.
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Your results
Enter your measurements to see your body fat estimate.
How to use this calculator
Choose your sex, enter your height (switch between ft/in and cm with the unit toggle), then measure your neck and waist with a flexible tape measure — plus your hip if you select female — and type the numbers in. Your estimated body fat percentage updates instantly as you type, along with your category and a gauge showing where you sit on the scale.
For the most consistent results, measure first thing in the morning before eating, with the tape snug but not compressing your skin. Measure the same way every time you recheck, and track the trend over weeks rather than fixating on a single reading.
How it works
The U.S. Navy method is an anthropometric estimate: it predicts body fat from a few circumference measurements and your height instead of imaging your body directly. The formulas (log₁₀, all measurements in inches) are:
- 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
Think of it this way: the formula compares your midsection (waist, plus hips for women) against your neck and height. A big waist relative to your neck and height suggests more body fat; a thicker neck suggests more overall muscle mass, which pulls the estimate down.
Important: this is an estimate, not a measurement. Compared with a DEXA scan, the Navy method is typically accurate to about ±3–4 percentage points for average adults. Very muscular, very tall, or older adults may see larger errors. It is a great free tool for tracking change over time — but it is not medical advice, and it cannot diagnose anything about your health.
Frequently asked questions
How accurate is the Navy body fat method?
For most people, the Navy method lands within about 3–4 percentage points of a DEXA scan, as long as you measure carefully and consistently. It is a solid free estimate, but it is still an estimate — it cannot match a lab scan for absolute accuracy.
Where exactly do I measure my waist?
Men should measure at the navel; women at the natural waistline (the narrowest part of the torso). Keep the tape horizontal, snug but not compressing the skin, and measure at the end of a normal exhale while standing relaxed.
Navy method vs DEXA scan — which is better?
A DEXA scan is more accurate because it directly images fat, muscle, and bone. The Navy method is free, instant, and great for tracking trends over time. Use the Navy method the same way each time and watch the direction of change rather than obsessing over the exact number.
How often should I recheck my body fat?
Every 2–4 weeks is plenty. Body fat changes slowly, and daily measurements just capture water and food fluctuations. Always measure at the same time of day under the same conditions.
Why does the formula need my neck measurement?
The neck measurement helps the formula tell muscular builds apart from higher-fat builds. A thick neck usually signals more overall muscle mass, so subtracting it from the waist corrects for people who are simply larger-framed rather than carrying more belly fat.
Is this calculator medical advice?
No. This tool is for general information and fitness tracking only. It is not a medical diagnosis or recommendation. If you have health concerns about your body composition, talk to a doctor or qualified health professional.