📏 Body Fat Calculator

Estimate body fat percentage from tape measurements (US Navy method).

About this tool

Estimates body fat percentage using the US Navy circumference method, which uses neck, waist, height, and — for women — hip measurements, plugged into a logarithmic formula developed and validated by the US Navy as a low-cost field alternative to more precise methods.

This method is a reasonable estimate for many people but is meaningfully less accurate than clinical methods like DEXA scans, hydrostatic weighing, or skinfold calipers — treat the result as a rough indicator, not a precise measurement.

Worked example

A male with a 38 cm neck, 85 cm waist, and 175 cm height gets an estimated body fat of roughly 15%.

How to use it

Select sex — the formula differs for men and women.
Measure neck and waist (and hip, for women) carefully with a tape measure, following standard measurement points.
Enter height and press Estimate body fat %.

Tips

Measure at the same time of day and in the same conditions each time for consistent tracking — hydration and food intake can shift circumference measurements slightly.
This method tends to be less accurate for people at the extremes of the body fat range (very lean or very high body fat) compared to average builds.
For a more precise measurement, DEXA scans and hydrostatic weighing are the clinical gold standards, though far less accessible than a tape measure.

FAQ

How accurate is the tape-measure method?

It's a reasonable field estimate that correlates fairly well with more precise methods for many people, but it can be noticeably off for individuals at unusual body compositions — it's a rough indicator, not a diagnostic measurement.

Why does the formula ask for different measurements for men and women?

The US Navy method uses separate validated formulas for male and female bodies, reflecting typical differences in fat distribution patterns between sexes.

Should I use this instead of a DEXA scan or calipers?

Only if those aren't accessible to you — this tape-measure method is a convenient estimate, not a replacement for clinical-grade measurement when precision genuinely matters.

From the blog: getting the most out of this tool

We included this tool with a clear disclaimer up front rather than skipping it, because the tape-measure method is genuinely useful as a free, at-home trend indicator over time, even though it's not going to match a lab-grade DEXA scan measurement to the decimal.

The more useful way to use a tool like this is tracking the trend over weeks or months with consistent measurement technique, rather than treating any single reading as a precise, standalone fact about your body.

📖 Want the fuller explanation?

See BMI vs Body Fat Percentage for the reasoning behind this calculation, with worked examples.