About this body fat percentage calculator
Estimate body fat percentage from a tape measure rather than a scale. This uses the US Navy circumference method: height and neck and waist for men, plus hip for women. Enter the measurements in centimetres or inches and you get a percentage and the general category it falls in. The arithmetic runs in your browser and nothing you enter is sent anywhere, which matters for measurements most people would not type into a site that keeps them. It is an estimate from three or four numbers, not a body composition scan, and the limitations below say how far that goes.
How the body fat percentage calculator works
The US Navy circumference method, in its metric form. For men, body fat % = 495 ÷ (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450. For women the hip measurement joins the waist: 495 ÷ (1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.221 × log₁₀(height)) − 450. Imperial measurements are converted to centimetres before the formula runs, so inches and centimetres give the same answer for the same body. Measure at the navel for the waist, below the Adam's apple for the neck, and at the widest point for the hip, with the tape snug and level and not compressing the skin — the method is sensitive to where the tape sits.
Body Fat Percentage Calculator examples
Male, 175 cm tall, 85 cm waist, 38 cm neck
About 16.9% body fat
The same man measured in inches: 68.9 in, 33.5 in, 15 in
The same answer — imperial input is converted before the formula runs
Female, 165 cm tall, 75 cm waist, 32 cm neck, 98 cm hip
A percentage using the female formula, which includes the hip measurement
A waist measurement smaller than the neck
Rejected — the formula has no meaningful answer there, so it says so rather than returning a number
Limitations & privacy
An estimate from a tape measure. Circumference methods carry a meaningful margin against a DEXA scan or hydrostatic weighing — individual results can be several percentage points out, and the method fits people with unusual builds, including very muscular or very lean ones, least well. It is derived from adult populations and is not appropriate for children. Where the tape sits changes the answer, so use the same placement each time if you are tracking a trend, and treat the direction of travel as more informative than any single number. This implements the US Navy formula. The Army maintains its own body composition standard, which is not the same and has changed over time; if you are being assessed against a service standard, use that service's current method rather than this. Nothing here is a medical assessment — a result that concerns you is a reason to speak to a clinician.
Inputs and results stay in this browser. Only tool identifiers are stored for your recently used tools. You can clear that history from the directory.
Body Fat Percentage Calculator: frequently asked questions
What formula does this use?
The US Navy circumference method, the one used in the Navy's body composition assessment. Men need height, neck and waist; women also need the hip measurement. The formulas are written out in the method section above so you can check the arithmetic.
Can I enter measurements in inches?
Yes. Switch Units to Imperial. Inches are converted to centimetres before the formula runs, so both give the same answer for the same body.
Is this the same as the Army body fat calculator?
No. This implements the Navy method. The Army maintains its own body composition standard, which differs and has changed over time. If you are being assessed against a service standard, use that service's current method — do not rely on this number for it.
How accurate is a tape-measure estimate?
Less accurate than a DEXA scan, and individual results can be several percentage points out. It fits unusual builds least well, including very muscular and very lean people. It is most useful for tracking a direction over time with consistent tape placement, rather than for a single definitive figure.
Where exactly do I measure?
Waist at the navel, neck just below the Adam's apple, hip at its widest point. Keep the tape snug and level without compressing the skin. The method is sensitive to placement, so being consistent matters more than being precise to the millimetre.
Are my measurements stored?
No. The calculation runs in your browser and nothing you type leaves your device.
Updated October 10, 2026