Body Fat Calculator

What is a body fat calculator?

A body fat calculator estimates what share of your total body weight is fat, expressed as a body fat percentage. Instead of scales or skinfold calipers, the tool above uses the US Navy circumference method — a tape-measure technique developed by the Naval Health Research Center that needs only a few measurements in centimetres. You enter your height, neck and waist (women also add a hip measurement), and it returns a single percentage plus a fitness category.

Body fat percentage is often more meaningful than weight alone. Two people at the same weight can carry very different amounts of fat and muscle, so a body fat estimate gives a clearer picture of body composition than the bathroom scale or even BMI, which cannot tell muscle from fat.

How does the body fat calculator work?

This calculator uses the US Navy circumference formula, which applies the base-10 logarithm (log₁₀) to your tape measurements in centimetres. The equation differs by sex:

• 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

The terms are simple:

• height — standing height in centimetres.
• neck — circumference around the neck, just below the larynx, in cm.
• waist — circumference at the navel (men) or the narrowest point (women), in cm.
• hip — circumference at the widest point of the hips, in cm (women only).
• log₁₀ — the base-10 logarithm; for example log₁₀(47) is about 1.6721.

Because the formula takes the logarithm of waist − neck (men) or waist + hip − neck (women), that combined value must be positive. In practice that means waist must be larger than neck for men, or waist + hip must be larger than neck for women, or the calculation has no valid result. All measurements are entered in centimetres, and the output is a body fat percentage.

Examples

Here are fully worked calculations that match the tool’s output exactly.

Example 1 — Man, height 178, neck 38, waist 85

• waist − neck = 85 − 38 = 47, so log₁₀(47) is about 1.6721
• log₁₀(178) is about 2.2504
• Denominator: 1.0324 − 0.19077 × 1.6721 + 0.15456 × 2.2504 = 1.0324 − 0.3190 + 0.3478 = 1.0612
• 495 ÷ 1.0612 − 450 = 466.45 − 450 = about 16.5% body fat (fitness range)

Example 2 — Man, height 180, neck 40, waist 90

• waist − neck = 90 − 40 = 50, so log₁₀(50) is about 1.6990
• log₁₀(180) is about 2.2553
• Working the formula through gives 495 ÷ denominator − 450 = about 18.4% body fat (fitness range)

Example 3 — Woman, height 165, neck 32, waist 75, hip 95

• waist + hip − neck = 75 + 95 − 32 = 138, so log₁₀(138) is about 2.1399
• log₁₀(165) is about 2.2175
• Working the women’s formula through gives about 27.4% body fat (average range)

Example 4 — Woman, height 168, neck 34, waist 82, hip 102

• waist + hip − neck = 82 + 102 − 34 = 150, so log₁₀(150) is about 2.1761
• log₁₀(168) is about 2.2253
• The women’s formula returns about 32.5% body fat (above average range)

Notice that for men the gap between waist and neck drives the result: a larger waist relative to the neck raises body fat. For women, the waist-plus-hip total relative to the neck plays the same role.

Body fat percentage categories

The tool labels your result against common adult reference bands. These ranges differ for men and women because women carry more essential fat. Use the row that matches your sex and percentage.

Category	Men	Women
Essential fat	2 – 5%	10 – 13%
Athletes	6 – 13%	14 – 20%
Fitness	14 – 21%	21 – 24%
Average	22 – 24%	25 – 31%
Above average	25% and over	32% and over

In Example 1, a man at 16.5% sits in the fitness band; in Example 3, a woman at 27.4% sits in the average band; and in Example 4, a woman at 32.5% falls into above average. These categories are general guides, not strict medical thresholds.

Common uses

A body fat estimate is useful in several everyday situations:

• Track recomposition. When you lose fat and gain muscle, your scale weight may barely move; body fat percentage shows the real change.
• Set a fitness goal. Aiming for the athlete or fitness band gives a clearer target than a round weight number.
• Compare with BMI. Body fat percentage explains why a muscular person can read as overweight by BMI yet have low fat.
• Re-measure over time. Take the same measurements every few weeks under the same conditions to watch the trend.

Tips and common mistakes

• Measure consistently. Use the same tape, the same spots, and ideally the same time of day; small tape differences shift the result by a percent or two.
• Keep the tape level and snug. Pull it taut without compressing the skin, and keep it horizontal around the body.
• Use centimetres. This tool expects all measurements in cm, so convert inches first (1 inch = 2.54 cm) before entering them.
• Waist must exceed neck. If you enter a waist smaller than your neck (or, for women, a waist plus hip below the neck), the formula cannot produce a value.
• Measure relaxed, not flexed. Do not suck in your stomach or tense your neck; measure in a natural, relaxed posture for a representative reading.

Limitations and notes

The US Navy method is quick and surprisingly good, but it is still an estimate based on circumferences, not a direct measurement of body fat. It assumes a typical relationship between where you carry size and how much fat you hold, so it can be off for very lean, very muscular, or unusually proportioned people, and for those carrying most of their size outside the measured areas. More precise methods such as DEXA scans, hydrostatic weighing or air-displacement plethysmography measure body composition directly and will not always agree with this figure. Results also depend heavily on accurate, consistent tape placement.

Health disclaimer: This body fat calculator is provided for general information and education only. It is not medical, nutritional or fitness advice, and it is not a substitute for professional assessment. Consult a qualified healthcare professional before making decisions about your health, diet or training.

For more body and fitness self-checks, try the BMR calculator to estimate calories burned at rest, the ideal weight calculator for a target weight range, the BMI calculator to gauge weight for height, or the water intake calculator for daily hydration, and browse the full health & medical category for more tools.