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Body Fat Calculator

The US Navy circumference method estimates body fat percentage with nothing but a tape measure: height, neck, and waist for men, plus hips for women. It was developed for the Navy's body composition assessment program and gives a serviceable estimate without calipers or a scan — provided the tape is placed consistently, since small measurement differences move the result.

Body fat
22.2%
Average
About 22.2% body fat — the Average range
US Navy tape estimate, categorized by sex; it tends to read high on the very lean and muscular, so use it for the trend rather than a precise figure.
Where you sit
US Navy classification · male
22.2%
Essential
Athlete
Fitness
Average
Obese
Inputs
Sex
Sex
Your measurements (cm)
Height (cm)
Neck (cm)
Waist (cm)
Technique decides accuracy
A 2 cm error at the waist can swing the result several points. Keep the tape snug but not compressing, don't hold your breath or suck in, and measure at the same time each day.
The Navy method is an estimate
It tends to read high on the very lean and very muscular. Use it for a trend and for composition context alongside BMI; a DEXA scan is the accurate reference.
Ask a follow-up
Uses your inputs above
22.2% body fat. Want to try a variation?

The math

Reviewed 2026
Formula
Navy: 86.01·log10(waist−neck) − 70.04·log10(height) + 36.76
Measurements in cm

Related calculators

BMI
Ideal weight

Example: how body fat is calculated

Step-by-step with default inputs

Suppose you put the default values into Body Fat Calculator:

Sex
Male
Height (cm)
178
Waist (cm)
84
Neck (cm)
38

Plug those into the formula Navy: 86.01·log10(waist−neck) − 70.04·log10(height) + 36.76 and the result is:

Body fat
22.2%

How to calculate body fat by hand

  1. Measure heightCm, neckCm at its narrowest point, and waistCm at navel level, all in centimeters; women also measure hipCm at the widest point.
  2. Men: subtract neck from waist and take log10 of the difference.
  3. Multiply by 86.01, subtract 70.041 x log10(height), then add 36.76.
  4. Women: compute 163.205 x log10(waist + hip - neck) - 97.684 x log10(height) - 78.387.
  5. The result is body fat as a percentage of total body weight.

How does the body fat calculator work?

The formulas are the US Navy circumference equations: for men, 86.01 x log10(waist - neck) - 70.041 x log10(height) + 36.76; for women, 163.205 x log10(waist + hip - neck) - 97.684 x log10(height) - 78.387, all measurements in centimeters. Circumference methods trade accuracy for accessibility — they infer fat from body geometry rather than measuring it directly, so results can drift for very lean, very muscular, or unusually proportioned bodies. Treat the output as a tracking estimate, useful for trends over time, rather than a clinical body composition measurement.

References: US Navy Body Composition Assessment.

Last reviewed July 2, 2026 · Editorial policy

Frequently asked questions

Where exactly do I measure for the Navy method?

Neck at its narrowest point and waist horizontally at navel level, with the tape snug but not compressing skin. Placement matters: around the default measurements, a single centimeter of waist shifts the result by close to a percentage point, so measure the same spots every time.

What do the category labels mean?

They are descriptive bands used by this calculator: for men, 6-14% is labeled athlete, 14-18% fitness, 18-25% average, above 25% obese; the female bands run about 7-8 points higher, with essential fat alone topping out at 14% for women versus 6% for men.

Why does the women's formula include hips?

Because the female equation was fit with an additional circumference to capture typical fat distribution — it uses waist + hip - neck inside the logarithm, with its own coefficients. Leaving hips out would make the male geometry assumptions apply where they fit worst.

What does this calculator assume?

Measurements in cm See the math card above for the full list.

How accurate is this body fat calculator?

The math is deterministic — the same inputs always produce the same output, and the formula is shown above. Accuracy of the answer for your situation depends on how well your inputs match reality and how well the formula models the question.

Is this a substitute for medical advice?

No. Health calculators give informational baselines from published formulas. For decisions about your body, talk to a clinician.

Guides

What is a healthy body fat percentage?Healthy body fat percentage ranges for men and women, by category — from essential fat to fitness to obese — and why it's often a better signal than BMI.