Body Fat Calculator (US Navy Method)
Estimate body fat percentage with the US Navy tape method. All you need is a soft tape measure and one minute.
Estimated body fat
- Category
- Fit
- Method
- US Navy tape
- Accuracy
- ±3-4%
- Re-check
- Every 2-4 wks
Worked examples
How the US Navy body fat formula works
The US Navy developed this tape-measure method in the 1980s as a fast, equipment-free way to screen body composition. It uses circumference measurements and height as a proxy for body density, then converts density to fat percentage via the Siri equation.
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) + 0.221 × log10(height)) − 450
All measurements are in centimeters. Studies comparing the Navy tape method to hydrostatic weighing and DEXA find it lands within ±3-4 percentage points for the average person, not lab-grade, but useful.
How to take the measurements
- Neck: Stand tall, look forward. Wrap the tape just below the larynx (Adam's apple).
- Waist (men): At the level of the navel, around the widest part.
- Waist (women): The narrowest point of the natural waist, usually a couple of inches above the navel.
- Hips (women): The widest part of the buttocks with feet together.
- Measure first thing in the morning, after the bathroom, before food and water. Take each measurement twice and average.
How to use your result
The number itself matters less than the trend. If you measure every 2-4 weeks under the same conditions, you'll see body composition change well before the scale moves. Combined with weekly average bodyweight, this is the most useful pair of data points for tracking a cut.
Worked examples
Example 1. 180 cm man, neck 38 cm, waist 84 cm. Waist − neck = 46. Plug it in: ≈ 15% body fat, fit range.
Example 2. 165 cm woman, neck 32 cm, waist 72 cm, hip 95 cm. Waist + hip − neck = 135. Result ≈ 24%, fit range.
Example 3. 175 cm man, neck 41 cm, waist 95 cm. Waist − neck = 54. Result ≈ 22%, average range.
Common mistakes
- Pulling the tape tight. The tape should sit on the skin without compressing it.
- Measuring at different times. Stomach contents and water move waist by an inch.
- Measuring after lifting. Wait 24 hours; trained muscle holds water.
- Skipping the hip measurement (women). The formula needs it.
- Treating it as lab-grade. It's a useful estimate, not a verdict.
FAQ
How accurate is the US Navy method?+
Around ±3-4% body fat compared to a DEXA scan for most people. It's not as precise as a lab test but it's free, repeatable, and good enough to track change over time.
Where exactly do I measure?+
Neck: just below the larynx, looking straight ahead. Waist: at the navel for men, at the narrowest point for women. Hips (women only): around the widest part of the buttocks. Use a soft tape, snug but not compressed.
Why is hip measurement required for women?+
The formula was derived from Navy personnel and adds the hip measurement for women to account for typical fat distribution differences. Skipping it makes the result invalid.
What body fat percentage is 'healthy'?+
Generally 10-20% for men, 18-28% for women is considered healthy. Athletic ranges run lower; essential body fat is about 3% for men and 12% for women.
How often should I measure?+
Every 2-4 weeks at the same time of day, ideally first thing in the morning after using the bathroom and before drinking water.
Why did my body fat go up after a heavy training week?+
Heavy training causes water retention, which inflates waist measurements. Don't measure within 24 hours of a hard session.
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