Body Fat Calculator
Measure your neck, waist and (for women) hips to estimate body fat percentage, fat mass and lean mass.
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Your weight alone does not say how much of you is fat and how much is muscle, bone and water. Body fat percentage does. This calculator uses the US Navy circumference method, which needs nothing more than a flexible tape measure, to estimate your body fat, fat mass and lean mass.
How to use the body fat calculator
- Choose centimeters and kilograms or inches and pounds.
- Select your sex.
- Enter your height and weight.
- Measure and enter your neck and waist. Women also enter their hips.
How to measure
- Neck: just below the larynx (Adam’s apple), with the tape sloping slightly down towards the front.
- Waist (men): horizontally at the level of the navel.
- Waist (women): at the narrowest point, usually a little above the navel.
- Hips (women): at the widest point of the buttocks.
Keep the tape snug but not compressing the skin. Stand relaxed, do not suck in, and take each measurement twice.
The US Navy formulas
With all measurements in centimeters:
Men: Body fat % = 495 ÷ (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450
Women: Body fat % = 495 ÷ (1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.22100 × log₁₀(height)) − 450The formulas estimate body density from your shape, and the 495 ÷ density − 450 part (the Siri equation) turns density into a fat percentage. If you enter inches, the calculator converts them to centimeters first.
Fat mass = Weight × Body fat % ÷ 100
Lean mass = Weight − Fat massWorked example
A man who is 180 cm tall and weighs 80 kg, with a 38 cm neck and an 85 cm waist:
- waist − neck = 47, and log₁₀(47) ≈ 1.6721
- log₁₀(180) ≈ 2.2553
- Body fat = 495 ÷ (1.0324 − 0.19077 × 1.6721 + 0.15456 × 2.2553) − 450 ≈ 16.1%
- Fat mass = 80 × 0.161 ≈ 12.9 kg, and lean mass ≈ 67.1 kg
- Category: Fit
A woman who is 165 cm tall, with a 33 cm neck, 72 cm waist and 98 cm hips, comes out at about 26.9%, in the Average range.
Body fat categories
These commonly used ranges come from the American Council on Exercise:
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletic | 6–13% | 14–20% |
| Fit | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Above average (obese range) | 25% and over | 32% and over |
Essential fat is the minimum needed for normal body function. Going below it is unhealthy.
Tips for reliable results
- Measure consistently. Same time of day, same spot, same tape. Morning, before eating, works best.
- Track the trend. A single reading can be off by a few points, but a series of readings shows real change well.
- Watch your waist too. A waist over about 102 cm (40 in) for men or 88 cm (35 in) for women is linked to higher health risk, whatever your body fat.
- Compare like with like. Smart scales, calipers and DEXA scans use different methods and give different numbers. Do not mix them when tracking progress.
This calculator gives an estimate for general information. It is not a medical assessment.
Frequently asked questions
How accurate is the US Navy body fat method?
For most people it lands within about 3–4 percentage points of a laboratory measurement such as a DEXA scan. It is less accurate for very lean, very muscular or very heavy people, and it depends heavily on measuring carefully.
What is a healthy body fat percentage?
Typical healthy ranges are roughly 14–24% for men and 21–31% for women. Athletes are often lower. Needs vary with age, and a little more body fat is normal as people get older.
Why do women need a hip measurement?
Women tend to store more fat around the hips and thighs, so the female formula adds the hip circumference to improve accuracy. The male formula uses only the neck and waist.
How often should I measure?
Every two to four weeks is enough. Day-to-day changes are mostly measurement noise and water. Measure at the same time of day, ideally in the morning before eating.
Is body fat percentage better than BMI?
It tells you more, because BMI cannot tell muscle from fat. A muscular person can have a high BMI and low body fat. Using both, along with waist size, gives the clearest picture.