Tape-measure method

Body Fat Calculator

Estimate body fat with the classic US Navy circumference method. It is fast, repeatable, and useful for tracking a trend — without pretending a tape measure is a medical scan.

No account No data upload Metric + imperial Works offline after load

Your measurements

Height (cm)

Neck (cm) Just below the larynx; tape level and snug

Waist (cm) At navel level, abdomen relaxed

Optional — add weight for fat/lean mass, BMI and target-weight projection. Add age for a second, rough BMI-based body-fat estimate.

Weight (kg)

Age (years)

Result

—% —

Estimated by circumference. Treat the direction over time as more useful than the decimal point.

0%45%

Best use: repeat the same measurement protocol weekly and compare the trend. A one-off reading can move simply because the tape was placed differently.

How to measure correctly

Use a flexible, non-stretch tape Keep it level and snug against the skin. Do not pull hard enough to compress tissue.

Neck Measure just below the larynx. Look straight ahead, shoulders relaxed, and do not flare the neck muscles.

Waist Men: measure horizontally at navel level. Women: measure at the natural/narrowest waist. Relax the abdomen and measure after a normal exhale.

Hips — women only Measure around the greatest protrusion of the buttocks, with the tape horizontal.

Repeat 2–3 times If repeated values disagree, re-check tape position and use a consistent average. Morning, before food or training, is a convenient repeatable routine.

Do not mix protocols If you change where you measure the waist or switch to a smart scale / DEXA, establish a new baseline instead of treating the numbers as interchangeable.

Body-fat reference categories

Common fitness-reference bands often reproduced from ACE classifications. These are orientation ranges, not diagnostic cut-offs.
Category	Women	Men
Essential / very low	10–13%	2–5%
Athletic	14–20%	6–13%
Fitness	21–24%	14–17%
Average / acceptable	25–31%	18–24%
Above this reference range	32%+	25%+

BMI is supporting context

BMI uses only height and weight. It cannot distinguish fat from muscle, so it should not replace a body-composition estimate.

Adult BMI category	BMI
Underweight	< 18.5
Healthy weight	18.5–24.9
Overweight	25.0–29.9
Obesity class 1	30.0–34.9
Obesity class 2	35.0–39.9
Obesity class 3	40.0+

Which body-fat method should you use?

Method	Best use	Main limitation
US Navy tape	Simple home trend	Technique + body-shape dependent
Smart scale / BIA	Frequent trend	Hydration can move the reading
Skinfold calipers	Trend with a skilled measurer	Operator skill matters heavily
DEXA	Detailed body-composition assessment	Cost, access, method-to-method variation
Air displacement / hydrostatic	Specialist testing	Less convenient and less accessible

Method transparency

US Navy circumference calculation

This version uses the classic body-density equations with circumference measurements in centimetres, then converts density to estimated body-fat percentage.

Male density = 1.0324 − 0.19077×log10(waist−neck) + 0.15456×log10(height) Female density = 1.29579 − 0.35004×log10(waist+hip−neck) + 0.22100×log10(height) Body fat % = 495 / density − 450

Derived values

Fat mass = weight × body-fat fraction Lean mass = weight − fat mass BMI = weight(kg) / height(m)² Projected target weight = lean mass / (1 − target BF fraction)

Optional BMI-based body-fat estimate

When weight and age are available, the calculator also shows the Deurenberg adult estimate as a rough comparison. It is a population equation, not an individual measurement.

BF% ≈ 1.20×BMI + 0.23×age − 10.8×sex − 5.4 (sex: male=1, female=0)

What can distort the result?

Tape placement, tape tension, posture, breathing, unusual body proportions, muscularity and fat distribution can all shift the estimate. The method does not directly measure visceral fat, bone density or metabolic health.

Accuracy and interpretation

The Navy result is an estimate, not a ground-truth percentage. Circumference methods can differ from DEXA or other techniques by several percentage points, and even DEXA values vary with machine, software and testing conditions.

The decimal is not the important part. If your result moves from 23.4% to 23.0%, that may be real change or simple tape-placement noise. A sustained trend across several consistent measurements is more meaningful.

Very low body fat is not automatically healthier. Essential-fat ranges are not performance targets, and chronically aggressive targets can be inappropriate.

This tool is for general information and fitness tracking. It is not medical advice or a medical device.

All calculations happen in your browser. Measurements are not sent anywhere.