Body Fat Calculator
Estimate body fat percentage using the US Navy circumference method.
Your figures
Result
How to use this tool
- Enter your own figures over the defaults — Weight, Height, Neck and the rest.
- The answer updates as you type. There is no button, and nothing is sent anywhere.
- Change one input at a time to see how sensitive the answer is to it.
Circumference methods are estimates with a typical error of three to four percentage points. They are useful for tracking change over time, less so for a single absolute number.
How it works
This takes 6 inputs — weight, height, neck, waist, hip (women only), sex at birth — and returns estimated body fat, fat mass, lean mass and method. The whole calculation happens in this page as you type: there is no submit button, no request, and nothing stored.
A worked example
Worked through with the figures the page already has in it: weight of 70 kg and height of 175 cm, and the rest as shown, giving estimated body fat of 16.9%. These numbers come from running the calculator’s own code, not from being typed in here, so they cannot drift away from what you see on screen.
Starting from:
- Weight: 70 kg
- Height: 175 cm
- Neck: 38 cm
- Waist: 85 cm
- Hip (women only): 95 cm
- Sex at birth: Male
| Result | Value |
|---|---|
| Estimated body fat | 16.9% |
| Fat mass | 11.9 kg |
| Lean mass | 58.1 kg |
| Method | US Navy circumference formula — an estimate, not a body scan. |
Body Fat Calculator — frequently asked questions
How accurate is this?
Typically within three to four percentage points of a DEXA scan. Best used to track direction over weeks rather than as an exact figure.
How should I measure?
Use a flexible tape, relaxed, without compressing the skin. Waist at the navel for men, at the narrowest point for women. Measure at the same time of day each time.
What is a healthy body fat percentage?
Broadly 10–20% for men and 18–28% for women, varying by age and source. Essential fat sits around 3% for men and 12% for women.
Is this calculator free?
Yes, with no account, no limits and no data collection. It runs entirely in your browser.
Should I rely on this for a financial or medical decision?
No. It is a planning estimate built on standard formulas and stated assumptions. For decisions that matter, speak to a qualified professional who can account for your full circumstances.
Is this calculator accurate?
The arithmetic is exact — it uses the standard formula. What limits accuracy is the assumptions: the figures you enter, and factors the formula does not model such as fees, taxes and rule changes.
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Nothing is sent anywhere. The figures you type stay in this page and are never transmitted or stored — how that works.
Disclaimer. The formula is exact; the answer is only as good as the figures and assumptions above. Not financial, tax, medical or legal advice. Full disclaimer.