💪 Body Fat Calculator

Estimate your body fat percentage using the U.S. Navy circumference method — one of the most accessible and validated non-lab techniques. Enter neck, waist, and hip (women) measurements for an accurate result.

Free U.S. Navy Method Metric & Imperial

Your Measurements

ℹ Women need an additional hip measurement. The formula differs by sex.

Body Measurements
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ft
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lbs
kg
Circumference Measurements

📍 Measure just below the larynx (Adam's apple), perpendicular to neck axis.

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📍 Measure at the widest point of the hips/buttocks, parallel to floor.

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Use a flexible tape measure

Keep it snug but not tight. Don't compress the skin.

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Neck — below the larynx

Measure at or just below the Adam's apple, perpendicular to the neck axis. Tilt head straight forward.

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Waist — at the navel (men) / narrowest (women)

Men: measure at the navel. Women: measure at the narrowest part of the torso. Exhale normally before measuring.

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Hip — widest point (women only)

Measure around the widest part of the hips and buttocks, parallel to the floor.

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Waist must be larger than neck

The Navy formula requires waist > neck (men) and waist + hip > neck (women). If these aren't met the formula cannot compute.

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U.S. Navy Method

Validated circumference-based formula used by the U.S. military

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BF% Categories

Essential / Athletes / Fitness / Average / Obese scale

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Fat & Lean Mass

See how much of your weight is fat vs lean tissue

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What-If Scenarios

Weight at 5%, 10%, 15% lower body fat targets

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BMI Included

Body Mass Index cross-reference with weight

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Measure Guide

Step-by-step instructions for accurate measurements

📐 U.S. Navy Formula

♂ Male: 495 ÷ (1.0324 − 0.19077×log(waist−neck) + 0.15456×log(height)) − 450

♀ Female: 495 ÷ (1.29579 − 0.35004×log(waist+hip−neck) + 0.22100×log(height)) − 450

All measurements in inches. log = log base 10.

The US Navy circumference formula in full

The method uses logarithms of body circumferences to estimate fat percentage, with separate equations for men and women. For men, body fat percentage equals 495 divided by (1.0324 minus 0.19077 times the base-ten logarithm of waist minus neck, plus 0.15456 times the base-ten logarithm of height), minus 450. For women, it equals 495 divided by (1.29579 minus 0.35004 times the logarithm of waist plus hip minus neck, plus 0.22100 times the logarithm of height), minus 450.

All circumferences are expressed in inches, so metric entries are converted before the formula is applied. The waist term is the key driver, because abdominal girth relative to neck size tracks visceral and subcutaneous fat closely, while the height term normalises for frame size.

The formula requires waist to exceed neck for men, and waist plus hip to exceed neck for women; otherwise the logarithm has no valid value and no result can be produced. Fat mass is then body weight times the percentage, and lean mass is the remainder.

Worked example: a man of 180 cm and 80 kg

Take a man 180 cm tall weighing 80 kg, with a neck of 38 cm and a waist of 94 cm measured at the navel. Converted to inches those become 70.87 for height, 14.96 for neck and 37.01 for waist.

Waist minus neck is 22.05 inches, and the base-ten logarithm of that is 1.3433. The logarithm of 70.87 is 1.8505. Substituting: 0.19077 times 1.3433 is 0.2563, and 0.15456 times 1.8505 is 0.2860. The bracket becomes 1.0324 minus 0.2563 plus 0.2860, which is 1.0621. Dividing 495 by 1.0621 gives 466.05, and subtracting 450 leaves 16.05 percent body fat.

That places him in the fitness band for men, which runs roughly 14 to 17 percent. Applying the percentage to his weight gives a fat mass of 12.8 kg and a lean mass of 67.2 kg. His BMI is 80 divided by 1.8 squared, which is 24.7, near the top of the healthy range despite the favourable body fat figure.

Measuring accurately and reading the result

Accuracy depends almost entirely on your tape work. Measure first thing in the morning before eating, keep the tape level and snug without compressing the skin, and breathe out normally rather than holding your stomach in. Men measure the waist at the navel; women measure at the narrowest point. Hip measurement for women is taken at the widest point of the buttocks. Repeat each measurement three times and use the average, because a single centimetre on the waist can shift the result by around one percentage point.

The Navy method typically falls within three to four percentage points of a DEXA scan, which is good for a tape measure but not precise enough to chase small changes. Its value is in the trend: measure under identical conditions every two to four weeks and watch the direction rather than any single figure. It can misread very muscular builds and people carrying fat atypically.

BMI is included only as a cross-reference, since it cannot distinguish muscle from fat. Treat the figure as a guide to track, not a clinical diagnosis.

Frequently Asked Questions

It typically lands within three to four percentage points of a DEXA scan, which is reasonable for a tape-measure method requiring no equipment. Accuracy drops for very muscular builds and for people whose fat distribution is unusual. Use it to track direction over weeks rather than to pin down an exact percentage.
Measure the neck just below the larynx, with the tape sloping slightly downward at the front. Men measure the waist horizontally at the navel; women measure at the narrowest point of the torso. Keep the tape level and snug without compressing the skin, and breathe out normally rather than holding your stomach in.
Commonly cited bands put men at 6 to 13 percent for athletes, 14 to 17 percent for fitness, 18 to 24 percent as average and 25 percent or above as obese. Women's bands sit about ten points higher because of essential fat requirements. These are general population guides, not clinical thresholds.
The female equation includes hip circumference because women typically store more fat around the hips and thighs, which the waist measurement alone would miss. The male formula relies on waist minus neck, since men store proportionally more fat abdominally. Using the wrong equation produces a badly skewed result.
For assessing an individual, generally yes. BMI uses only height and weight, so it cannot distinguish muscle from fat and classifies many trained athletes as overweight. Body fat percentage estimates composition directly. BMI remains useful for population statistics and appears here as a cross-reference rather than a competing verdict.