Body Fat Calculator
The US Navy method estimates body fat from tape measurements — waist and neck for men, plus hips for women — against height, using a logarithmic formula. It typically lands within 3–4 percentage points of a DEXA scan, which is accurate enough to track change over time even when the absolute figure is off.
Enter your tape-measure numbers — your body fat % updates as you type. This tool gives a general estimate from the published U.S. Navy method; it is not medical advice or a diagnosis.
How this calculator works
This tool uses the U.S. Navy body fat method, a tape-measure formula developed for military fitness testing. The core signal is your waist measurement relative to your neck — for women, hip is added too, since fat distribution differs by sex — with height as a scaling correction. Because the published formula was built on inches, any centimeter values you enter are converted internally (1 inch = 2.54 cm) before the calculation. Being upfront about its limits: this is a real published method, but it's still an estimate. Validation studies put its typical margin of error around ±3–4 percentage points versus a DEXA scan, so treat the result as a useful ballpark, not a lab-grade number.
Worked example
A male, height 70 in, neck 15 in, waist 34 in: waist − neck = 19, so log₁₀(19) ≈ 1.278754, and log₁₀(70) ≈ 1.845098. Plugging into 495 ÷ (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450 gives a denominator of about 1.073631 and a body fat estimate of ≈11.1%, which falls in the "athletes" reference range for men.
Frequently asked questions
How accurate is the U.S. Navy method?
It's an estimate, not a lab measurement. Published validation studies put its typical margin of error at around ±3–4 percentage points compared to a DEXA scan (the imaging-based clinical reference). That's close enough to track trends over time, but not precise enough to treat a single reading as exact.
Why do neck and waist measurements matter?
The core signal in the Navy method is the waist-to-neck relationship: your neck circumference is used as a rough proxy for a lean baseline, and how much larger your waist is than that baseline correlates with abdominal fat. Height is added as a scaling correction. It's a clever shortcut with a tape measure, not a direct fat measurement.
Is the method different for women?
Yes. The men's formula uses waist minus neck; the women's formula adds a hip measurement — waist plus hip minus neck — because fat distribution and the waist-to-neck relationship differ by sex. That's why this calculator asks for hip circumference only when you select "female."
What's a more accurate method than this?
Clinical options like a DEXA scan or hydrostatic (underwater) weighing directly measure body composition and are far more precise. Skinfold calipers, read by a trained professional, are a more accurate tape-and-hands option than this formula. This calculator is a free, instant estimate — not a replacement for those methods.
Is this a medical diagnosis?
No. This tool produces a general estimate from a published formula, not medical advice or a diagnosis. Body fat percentage is one data point among many; a full health picture needs a qualified professional.