Body mass index (BMI) tells you how heavy you are for your height, but it cannot tell muscle from fat. The US Navy Body Fat Calculator uses the circumference method — a simple tape-measure equation developed by the US Naval Health Research Center to screen service members on the "tape test." With nothing but a flexible measuring tape and a few minutes, you can estimate your body fat percentage at home, in your gym locker room, or at a military recruiting station, no calipers or DEXA scan required.
Enter your gender, neck, waist, hip (women only), and height in inches. The result card returns your estimated body fat percent, the Navy service limit for your gender (26% for men, 36% for women), and your gap to that limit — a negative number means you are under the limit, a positive number means you are over it.
How to Use
- Pick your Gender. Men use the neck-and-waist equation; women use neck, waist, and hip. This swaps the coefficients automatically.
- Measure your neck. Wrap the tape just below the larynx (Adam's apple), slanting slightly downward along the natural jaw angle. Take the measurement relaxed, not swallowing.
- Measure your waist. Men measure at the navel; women measure at the narrowest natural waistline. Keep the tape horizontal, level, and snug but not compressing the skin. Breathe out fully before reading.
- Measure your hip (women only). Take the largest circumference around the buttocks. Leave this field blank or zero if you selected male — it is ignored in the male equation.
- Enter your height in inches, standing upright against a wall with no shoes.
- Read the result: your estimated body fat percent, the Navy service limit for your gender, and your gap to that limit. A negative gap means you are under the limit; a positive gap means you need to trim down.
For the most repeatable number, take each measurement two or three times and average the readings. A half-inch error at the waist can shift the result by a percent or two, because the formula weights the waist-to-neck difference most heavily.
The US Navy Formula
The method estimates body density from log-transformed circumferences, then converts density to body fat percent using the standard Siri equation (the 495 and 450 constants).
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) + 0.22100 × log₁₀(height)) − 450
All inputs are in inches, and the logarithms are base-10. The key ratio driving the result is waist minus neck for men, and waist plus hip minus neck for women. A larger waist relative to the neck and height raises the estimate; a thicker neck (which includes muscle and skeleton) lowers it.
Worked example — a man with a 15-inch neck, 35-inch waist, and 70-inch height: waist − neck = 20 inches. log₁₀(20) ≈ 1.301 and log₁₀(70) ≈ 1.845. The denominator works out to about 1.069, so 495 ÷ 1.069 − 450 ≈ 12.9% body fat.
How to Read Your Number
The American Council on Exercise (ACE) reference bands give context to the raw percent:
- Essential fat — men 2–5%, women 10–13%. The minimum fat required for hormonal and life-sustaining function.
- Athletes — men 6–13%, women 14–20%.
- Fitness — men 14–17%, women 21–24%.
- Acceptable — men 18–24%, women 25–31%.
- Obese — men 25%+, women 32%+.
The US Navy service limits are roughly 26% for men and 36% for women (the exact cutoff varies slightly by age and service branch). The result card shows that limit and your gap to it. A gap of −13.12 points means you are 13.12 percentage points under the male limit; a gap of +2 means you are 2 points over and need to trim the waist measurement.
Examples
Example 1 — The worked male default. A man measures a 15-inch neck, 35-inch waist, and is 70 inches tall. Plugging in gives about 12.9% body fat, a Navy limit of 26%, and a gap of −13.1 points — comfortably under the male tape-test cutoff.
Example 2 — A female candidate. A woman measures a 13-inch neck, 36-inch waist, 44-inch hip, and is 65 inches tall. The female equation (waist + hip − neck = 67 inches) returns about 18.2% body fat, a female Navy limit of 36%, and a gap of −17.8 points.
Example 3 — Failing the tape test. A man with a 15-inch neck but a 42-inch waist at 70 inches tall gets roughly 26–28% body fat, crossing the 26% male limit with a gap of about +1 to +2 points. Trimming the waist by a couple of inches is usually enough to flip the gap back below zero.
FAQ
What measurements do I need for the Navy body fat test?
You need a flexible tape measure and four numbers in inches: neck, waist, height, and — for women only — hip. Men do not need a hip measurement. Measure the neck just below the larynx, the waist at the navel (men) or narrowest point (women), and the hip around the largest buttocks circumference.
How accurate is the US Navy body fat calculator?
The circumference method is an estimate, not a laboratory measurement. It typically agrees with DEXA or hydrostatic weighing within about ±3–5 percentage points for most adults, but it can misclassify very muscular, very lean, or elderly bodies because it does not directly measure density. It is designed for screening, not for diagnosing health conditions.
What is a good body fat percentage for men?
On the ACE scale, men in the Fitness band carry about 14–17% body fat, Athletes 6–13%, and Acceptable 18–24%. Below 6% is essential fat territory and can be unhealthy unless you are a competing athlete. The US Navy cutoff for men is around 26%.
What is a good body fat percentage for women?
Women naturally carry more essential fat. The Fitness band is roughly 21–24%, Athletes 14–20%, and Acceptable 25–31%. Below 14% begins to suppress hormonal function. The US Navy female service limit is around 36%.
Why does the formula subtract the neck from the waist?
Because the neck measures bony structure and muscle that are not fat, while the waist measures abdominal fat. Subtracting neck from waist removes the skeleton and muscle baseline, so a muscular person with a thick neck is not unfairly penalized. The result is then normalized against height using a log scale.
Can I use centimeters instead of inches?
The coefficients in this equation are calibrated for inches. If you measure in centimeters, convert to inches first (divide by 2.54) before entering the numbers — mixing units will produce a wrong percentage. Every field on this page expects inches.
Does the Navy body fat test replace BMI?
It complements it. BMI still drives many fitness and insurance thresholds, but the tape test specifically estimates fat mass, so a heavily muscled athlete who reads as "overweight" on BMI may easily pass the Navy body fat standard. Use both together for a fuller picture.
Disclaimer
This Navy body fat calculator is provided for informational purposes only and is not medical advice. Estimates come from the US Navy circumference equation and are subject to measurement error; actual body composition varies by training, hydration, age, and body type. Do not use these results to diagnose, treat, or manage any medical condition, and consult a qualified physician or registered dietitian before making changes to your diet or training based on this estimate. For our editorial standards see the About page, and for data handling see the Privacy Policy; we do not store the body measurements you enter on this page.