Navy Body Fat Calculator

How to measure for the Navy body fat calculator

Use a flexible tape and measure against the skin without compressing it. This calculator implements the traditional neck-and-circumference method, described in the National Academies’ account of military body-composition methods. It is an educational tool, so it carries no authority over current service standards and will not tell you whether you pass one.

Take each measurement twice and keep your technique identical both times. The Metric and Imperial button switches all the tape measurements at once, and the height dropdown moves separately. Whichever you change, your existing entries are converted and not cleared.

The body fat formulas used here

All measurements are converted to centimetres. Let H be height, N neck, W waist and P hips. The logarithms are base 10.

Male: body fat % = 495 ÷ [1.0324 − 0.19077 × log10(W − N) + 0.15456 × log10(H)] − 450.

Female: body fat % = 495 ÷ [1.29579 − 0.35004 × log10(W + P − N) + 0.22100 × log10(H)] − 450.

These equations read your body proportions and infer a composition from them. No tape touches fat tissue, so the percentage is a prediction from shape. When two online calculators disagree by a point, the cause is usually a different equation version, rounded inputs, or a rounded final percentage.

Worked examples

Both rows exist to show the working. Neither one is a measurement anybody should aim at. The result badge uses broad descriptive fitness bands, and any diagnosis belongs to a clinician who can see more than your tape readings.

How accurate is the Navy method?

A tape estimate will differ from DXA or another laboratory method, and by how much depends on who you are. A study comparing circumference estimates with DXA in US Marines found the gap varied with both sex and body composition, which is why a single error figure for this method does not exist.

For tracking, measure under similar conditions with the same tape and the same technique. A one-point move over a fortnight is as likely to be your tape hand as your body, so give the trend a couple of months before you read anything into it.

Results are less useful during pregnancy, for children, and for anyone whose body proportions sit outside the groups these equations were developed on. Current military requirements change; consult the official Navy readiness guides for service assessments.

Body fat percentage versus BMI

The BMI calculator compares weight with height. This tool uses circumferences to estimate a percentage. Each one answers a narrow question, and a real health assessment covers far more ground than both together. Use the calorie calculator for a separate estimate of energy needs.

Convert body fat percentage to fat mass

Optional weight adds two results. Fat mass = body weight × body fat percentage ÷ 100. Fat-free mass is body weight minus fat mass. For example, a 70 kg body weight and a 20% estimate give 14 kg of fat mass and 56 kg of fat-free mass. For what that figure tends to look like on a man and on a woman, read what 20% body fat looks like.

Fat-free mass counts water, bone and organs alongside muscle, which puts it well above your muscle mass. Both derived masses are calculated from the unrounded tape percentage, so they inherit all of its uncertainty. Switching between kilograms and pounds converts the optional weight and both results.

Check the formula with your own measurements

The result panel shows each step for the selected male or female equation: conversion to centimetres, the circumference difference, base-10 logarithms and the final percentage. Enter body weight and the explanation also shows how the fat and fat-free masses are derived. Two decimals let you check the working, though your tape only reads to about a centimetre, so treat the second decimal as bookkeeping.

Copy or print your calculation

Open How your result is calculated and you get the unit conversions, the circumference difference, both logarithms and the final division, all worked through with your own measurements. The steps run the same equation as the headline percentage, with intermediate numbers rounded so they read cleanly.

Copy results puts your inputs, the labelled results, the calculation steps and the notes on your clipboard. Print / save PDF opens a report preview and then your browser’s print dialogue, where Save as PDF is usually one of the options. Read the report before you send it to anyone, because it carries every circumference you typed in. Reset example puts the sample values back and leaves your unit choices alone. All of this happens in your browser, and the tool keeps no history of your calculations.

Common questions

Do I need body weight for this calculator?

Weight is optional. Height and circumferences determine the Navy body fat percentage. Add body weight only if you also want estimates of fat mass and fat-free mass.

Can I enter inches?

Yes. Choose Imperial for the tape measurements and feet/inches for height. The code converts all measurements to centimetres before applying the equations.

Why does the female equation require hips?

Hips are an input to that equation, and a blank field is not a zero. Leave it empty and the formula has nothing to work with, so fill it in before reading the result.

Does this calculator tell me whether I pass the Navy assessment?

No. It is an educational implementation of the traditional tape equations. It does not apply current service eligibility rules, rounding procedures or assessment standards.

Why did the calculator ask me to check my measurements?

Blank, negative or inconsistent inputs cannot produce a usable estimate. Check the selected units, tape locations and values before trying again.

Written and maintained by Rowan Hale, the site author’s pen name. Updated September 13, 2026. No medical or dietetic qualification is claimed. Read our editorial policy or report a calculation error.