Body Fat Calculator
Calculate body fat percentage
Body Fat Calculator tool
Body Fat Calculator
Body Fat Calculator: key facts
- What it does
- Calculate body fat percentage
- Category
- Health & Fitness Calculators
- Cost
- Free, with no account, sign-up, or install.
- Your data
- Runs entirely in your browser — the files and text you enter are never uploaded to a server.
- Last reviewed
- . Report an incorrect result.
Understanding the Body Fat Calculator
Body fat percentage tells you more about composition than weight or BMI ever can — two people at the same weight can carry very different amounts of fat and muscle. This calculator estimates yours using the US Navy circumference method, which needs only a tape measure rather than calipers or a scan.
Fitness-minded people use it to track recomposition that the scale hides, when fat drops while muscle holds steady. Because the method relies on body measurements — neck, waist, and for women also the hips — alongside height, it gives a usable estimate at home without specialized equipment.
Getting a result
- Select your sex (this changes which measurements and formula are used).
- Enter your height in centimeters.
- Measure and enter your neck and waist circumference in centimeters.
- If you are female, also enter your hip circumference.
- Read your estimated body fat percentage, calculated with the US Navy method.
The US Navy circumference method
This estimates body fat from tape-measure circumferences rather than from weight, using the equations developed by Hodgdon and Beckett for the US Navy. The logic is that fat accumulates in predictable places, so the relationship between girth at the waist and girth at the neck carries information about composition that a scale cannot see.
Men need height, neck, and waist. Women additionally need hip circumference, because fat distribution differs enough that the female equation needs a third measurement to be usable. All inputs on this form are in centimetres, and the metric form of the equations is applied.
Measurement technique matters more than anything else here, because the equation is highly sensitive to the waist figure. Measure at the navel, with the tape level all the way round and snug but not compressing, at the end of a normal exhale. A centimetre of error at the waist moves the result by roughly a percentage point, so measuring the same way every time matters more for tracking than getting it perfect once.
- The default male entry — 175 cm height, 80 cm waist, 38 cm neck — estimates 12.87% body fat.
- The default female entry, adding a 95 cm hip measurement, estimates 24.34%. The two equations are not interchangeable and the same girths give very different answers.
- Widening the male waist to 90 cm while holding everything else moves the estimate to 20.66%, which shows how strongly the waist term drives the result.
Reasons to use it here
- It uses the US Navy circumference formula, so all you need is a tape measure — no calipers, scales, or lab equipment.
- It applies the correct sex-specific equation, including hip circumference for women, rather than a one-size-fits-all estimate.
- It reports a body composition figure that BMI cannot, distinguishing fat from overall weight.
- Measurements are processed in your browser and never uploaded.
How much to trust the number
The circumference method typically lands within three or four percentage points of a laboratory measurement, which is respectable for something requiring only a tape measure — but it is an estimate from a population regression, not a measurement of your body. Hydrostatic weighing, air displacement, and DEXA scanning are all more accurate and all require equipment.
The equations were fitted on military personnel, so they fit least well at the extremes: very lean, very heavy, heavily muscled, or elderly bodies all tend to be estimated less reliably. A muscular neck in particular deflates the male estimate, because the formula reads a thick neck as leanness.
The trend is worth far more than any single reading. Measured the same way, at the same time of day, under the same conditions, the direction of travel over weeks is genuinely informative even if the absolute figure carries a few points of error. Body fat percentage is also only one marker among many, and a figure that concerns you belongs in a conversation with a doctor rather than in a decision made alone.
Frequently Asked Questions
How accurate is the US Navy body fat method?
It is a reasonable estimate for most people and tracks changes well over time, but it is not as precise as a DEXA scan or hydrostatic weighing. Accurate, consistent tape measurements matter — measure at the same spots each time for reliable trend tracking.
Where exactly do I measure?
Measure the neck just below the larynx, the waist at the navel for men and at the narrowest point for women, and the hips at the widest point for women. Keep the tape snug but not compressing the skin, and stand relaxed.
What is a healthy body fat percentage?
Healthy ranges differ by sex and age, but general fitness guidelines often cite roughly 10–20% for men and 18–28% for women, with athletes typically lower. These are broad references, not medical thresholds, so consider them alongside other health markers.
Why does the female calculation need hip measurement?
The US Navy formula for women includes hip circumference because fat distribution differs by sex, and adding the hip measurement improves the estimate's accuracy. The male formula uses only neck and waist.
