How accurate is the US Navy method?

The US Navy circumference method is typically within 3-4% of more expensive methods like DEXA for most people. It is far more accurate than BMI for body composition because it accounts for where the fat sits.

Measure your neck below the larynx, your waist at the narrowest point for men or at the navel for women, and your hips at the widest point for women. Keep the tape snug but not compressing the skin.

Is my measurement data uploaded?

No. The entire calculation happens in your browser and none of your measurements leave your device.

Why do women need a hip measurement but men do not?

The Navy equations are sex-specific. The male formula uses only waist minus neck; the female formula adds hip circumference because women carry more fat around the hips, so omitting it would badly underestimate the result.

What is a healthy body fat percentage?

For men, the fitness range is roughly 14–17% and average is 18–24%; for women it is about 21–24% fitness and 25–31% average. Essential fat is around 2–5% for men and 10–13% for women — going below that is unhealthy.

Why does my waist size change the result so much?

The formula is driven by waist minus neck (men) or waist plus hip minus neck (women). Because the waist is the largest of these, a small change there moves the estimate the most — measure it consistently at the same point each time.

Can I lower body fat without losing weight?

Yes. Building muscle while keeping calories near maintenance replaces fat with lean mass, so the scale barely moves while your body fat percentage and waist measurement drop. That is why this estimate is more useful than weight alone.

Body Fat Calculator — Gera Tools

Body fat calculator — US Navy method

This calculator estimates your body fat percentage from a few tape-measure readings using the US Navy circumference method. Unlike BMI, which cannot tell muscle from fat, this method accounts for where the fat sits, making it far more useful for tracking body composition during a cut or recomposition. All you need is a soft tape measure.

How it works

The Navy formula works in inches, so metric inputs are divided by 2.54 first. It then applies a base-10 logarithmic regression that differs by sex:

Men: 86.01 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76
Women: 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387

The result is matched to the ACE (American Council on Exercise) category bands. Measure the neck below the larynx, the waist at the navel (women) or narrowest point (men), and the hips at their widest point (women).

Example

A man 70 in tall with a 15 in neck and 33.5 in waist:

86.01 × log₁₀(33.5 − 15) − 70.041 × log₁₀(70) + 36.76 = 86.01 × 1.267 − 70.041 × 1.845 + 36.76 ≈ 16.6% → Fitness

Category	Men	Women
Essential fat	2–5%	10–13%
Athletes	6–13%	14–20%
Fitness	14–17%	21–24%
Average	18–24%	25–31%
Above average	25%+	32%+

Everything is computed in your browser — none of your measurements leave your device.