Estimate your body fat percentage with nothing but a tape measure, using the US Navy circumference method. Enter your height, neck, waist and (for women) hip measurements in inches or centimetres.
Body Fat Calculator
How the Body Fat Calculator Works
Body fat percentage is the share of your weight that is fat, as opposed to muscle, bone, organs and water. It tells you more about body composition than weight or BMI alone: two people of identical height and weight can look and be very different if one carries more muscle. People use this estimate to track fat loss without being misled by the scale, since a good training month can add muscle while fat drops, leaving weight unchanged.
This calculator uses the US Navy circumference method, developed for estimating body fat from tape measurements alone. For men, it combines waist and neck measurements with height: body fat % = 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76, with all measurements in inches. For women it adds the hips: 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387. The logic is that neck size tracks lean mass while waist size grows with fat stores, so the difference between them is a surprisingly good fat signal. You can enter inches or centimetres; the calculator converts centimetres to inches before applying the formulas.
Your result is a percentage plus a category, and the calculator uses these bands. For men: below 2% is below the essential range, 2–5% is essential fat, 6–13% athletes, 14–17% fitness, 18–24% average, and 25% or more the obese range. For women, whose bodies naturally carry more essential fat: under 10% is labelled essential fat, 10–13% athletes, 14–20% fitness, 21–24% average, 25–31% high, and 32% or more the obese range. Measure carefully — a centimetre of tape error can shift the result by about a percentage point.
How to Use This Calculator
- Use a flexible tape measure on bare skin or thin clothing, standing relaxed — do not pull your stomach in.
- Height: measure without shoes, standing straight.
- Neck: measure just below the Adam’s apple, tape angled slightly downward to the front.
- Waist: men measure horizontally at the navel; women measure at the narrowest point of the natural waist. Keep the tape snug but not compressing the skin.
- Hips (women only): measure at the widest point of the hips and buttocks.
- Enter everything in one unit system, press Calculate, and for tracking progress re-measure under the same conditions every few weeks.
Example
A man who is 70 inches tall (5′10″), with a 15-inch neck and a 34-inch waist: body fat = 86.010 × log₁₀(34 − 15) − 70.041 × log₁₀(70) + 36.76 ≈ 17.5%, which lands in the Fitness category for men.
A woman who is 65 inches tall, with a 12-inch neck, 28-inch waist and 36-inch hips: the formula gives ≈ 24.6%, which this calculator places in the Average band for women (21–24.9%). Both examples show why the tape must be consistent: one inch more on the waist would raise each estimate noticeably.
Understanding Your Result
The categories describe ranges seen across the general population, with the “fitness” and “athletes” bands reflecting people who train regularly. Essential fat is the minimum the body needs to function — trying to go below it is dangerous, not admirable — and it is higher for women because of reproductive biology. Most health guidance focuses less on chasing the lowest possible percentage and more on avoiding the high ranges, where risk of metabolic disease climbs, and on the trend over time.
Accuracy-wise, the Navy method is generally considered to land within roughly 3–4 percentage points of more expensive methods such as DEXA scans for most people, provided the tape work is careful. It can misread very lean athletes, people who carry fat unusually (for example mostly on the thighs), and anyone whose neck is unusually muscular. Treat the number as a good estimate for tracking your own change — same tape, same spots, same time of day — rather than a precise medical measurement, and see a professional if you need an exact assessment.
Small technique details make a real difference. Take each measurement twice and use the average if the two readings differ; if they differ twice in a row, take a third and use the middle value. Breathe normally and measure at the end of a relaxed exhale, not with your chest puffed out or stomach braced. Measuring first thing in the morning, before food, also removes one source of day-to-day wobble from the waist reading.
Body Fat Calculator FAQs
How accurate is the Navy tape method?
For most people it comes within about 3–4 percentage points of laboratory methods when measurements are taken carefully. Consistent measuring technique matters more than the formula for tracking change over time.
Why does the formula use my neck measurement?
Neck size correlates with lean body mass and changes little with fat gain, while waist size grows as fat is stored. Comparing the two lets the formula separate fat from frame size reasonably well.
Where exactly should women measure the waist?
At the natural waist — the narrowest part of the torso, usually just above the navel — with the tape level and snug. Measuring at the navel instead is the most common cause of inflated readings.
What body fat percentage should I aim for?
There is no single right answer. Many adults feel and perform well in the fitness or average bands. Chasing the athlete or essential ranges is unnecessary for health and hard to sustain — focus on a range you can maintain comfortably.
Can this calculator be used for children or teenagers?
No. The Navy equations were developed and validated on adults. Children’s body composition changes rapidly with growth and needs age-specific assessment by a professional.
Related calculators: BMI Calculator, BMR Calculator, Ideal Weight Calculator.