Body Fat Calculator

How this body fat calculator works

Enter your sex, height, and a few circumference measurements (neck, waist, and hip for women) to estimate your body fat percentage using the US Navy method, a tape-measure-based formula developed for military fitness assessments that doesn’t require special equipment.

The US Navy method formula

Men: % body fat = 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450
Women: % body fat = 495 ÷ (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450

All measurements are in centimeters. Measure your neck just below the larynx, your waist at the navel, and (for women) hips at the widest point.

Step-by-step

Measure neck, waist, and (for women) hip circumference in centimeters.
For men, subtract neck from waist. For women, add waist and hip, then subtract neck.
Take the base-10 logarithm of that result, and separately of your height.
Plug both log values into the formula for your sex to get the density factor.
Divide 495 by that factor, then subtract 450 to get your body fat percentage.

Worked example

A man with a 38 cm neck, 85 cm waist, and 175 cm height:

Waist − neck: 85 − 38 = 47 cm
log10(47) ≈ 1.672, log10(175) ≈ 2.243
Density factor: 1.0324 − (0.19077 × 1.672) + (0.15456 × 2.243) ≈ 1.060
Body fat: (495 ÷ 1.060) − 450 ≈ 16.9%

A body fat percentage around 14-17% is generally categorized as “fitness” level for men.

Common mistakes

Measuring inconsistently. Small differences in where you place the tape (too tight, wrong height on the waist) can shift the result noticeably.
Using inches instead of centimeters without converting, which produces a meaningless result.
Forgetting the hip measurement for the women’s formula, which requires waist plus hip, not waist alone.
Treating the estimate as lab-grade precision. The Navy method is a field estimate, typically within a few percentage points of more precise methods like DEXA scans.

Tips

Measure at the same time of day (ideally morning, before eating) for consistent tracking over time.
Use a flexible tape measure snug against the skin but not compressing it.
Track the trend over weeks rather than obsessing over any single reading.

How accurate is the US Navy body fat method?

It’s generally accurate within a few percentage points compared to more precise lab methods like DEXA scans, making it a reasonably reliable field estimate without special equipment.

Do I need different measurements as a woman?

Yes, the women’s formula adds a hip circumference measurement in addition to neck and waist, since body fat distribution differs by sex.

What’s a healthy body fat percentage?

Healthy ranges are typically cited as roughly 10-20% for men and 18-28% for women, though ranges vary by age and source, and athletes often fall below these general ranges.

Why does this method use neck and waist instead of skinfold calipers?

The Navy method was designed for quick field assessments without specialized equipment, using simple tape-measure circumferences instead of the calipers required for skinfold-based methods.