How to Calculate Body Fat Percentage (Navy Method)

Your weight on the scale does not tell you how much of your body is fat versus muscle, but body fat percentage does. The U.S. Navy circumference method estimates it from a few tape measurements, no calipers or scans required. This guide explains the method and walks you through the Body Fat Calculator, which gives you your body fat percent and category for men and women in seconds. It is free, private and runs entirely in your browser. It is an estimate, not a medical diagnosis.

How the Navy body fat method works

The U.S. Navy method estimates body fat from body measurements that correlate with fat distribution, using only a tape measure and your height. For men it uses neck and waist; for women it adds the hips. The formulas are:

Men: body fat % = 86.010 x log10(waist - neck) - 70.041 x log10(height) + 36.76

Women: body fat % = 163.205 x log10(waist + hip - neck) - 97.684 x log10(height) - 78.387

Measurements are in inches and the logarithm is base 10. It is an estimate, not a direct measurement like a DEXA scan, but it is quick, repeatable and free.

How to use the Body Fat Calculator

Estimate your body fat in under a minute:

1. Open the Body Fat Calculator.
2. Choose your sex and enter your height.
3. Measure and enter your neck and waist (and hips if female).
4. Read your estimated body fat percentage and category.

Measure with a flexible tape, snug but not compressing the skin. Take the waist at the navel, the neck just below the larynx, and the hips at the widest point. Measure at the same time of day for consistent results over time.

A worked example

Take a man who is 70 inches tall with a 38-inch waist and a 16-inch neck.

• Waist minus neck: 38 - 16 = 22 inches
• log10(22) is about 1.342; log10(70) is about 1.845
• Body fat % = 86.010 x 1.342 - 70.041 x 1.845 + 36.76
• This works out to roughly 23%

That places him in the average range. If he trimmed his waist to 34 inches, the estimate would drop to around 16%, well into the fitness range, showing how sensitive the number is to waist size.

Body fat categories

The American Council on Exercise publishes commonly used categories. They differ by sex because women carry more essential fat:

Use these as a guide rather than a strict target. Trends over time matter more than a single reading.

Use cases and related tools

Tracking body fat percentage is useful when:

• You are losing fat and want to confirm you are keeping muscle
• The scale stalls but your body composition is still improving
• You are setting a fitness or athletic goal
• You want a fuller picture than weight or BMI alone

Pair it with the BMI Calculator for a quick height-to-weight check and the Calorie Calculator to plan your daily intake. Browse more in calculators.

Tips, limits and privacy

Keep these points in mind:

• The tape method is an estimate. Expect a margin of a few percentage points versus a DEXA scan.
• Consistency beats precision. Measure the same way each time and watch the trend.
• It does not work well for very muscular or very lean people, where the assumptions break down.

The Body Fat Calculator runs entirely in your browser, so your measurements are never uploaded or stored. It is informational only and not medical advice; consult a professional for health decisions. See all tools for more.