Body Fat Calculator — Free Online Tool
Estimate body fat % using the US Navy tape-measure method. · No signup · Works on mobile
100% private: your data is processed in your browser. Nothing is uploaded to our servers.
How to use the body fat calculator
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Measure your neck at its narrowest point and waist at the navel with a tape measure (women: also hips at the widest point).
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Enter the measurements plus your height and weight.
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See your body fat %, fat mass, lean mass, and category instantly.
What does this tool do?
This free body fat calculator estimates your body fat percentage using the US Navy circumference method — no calipers or scans needed. Enter your height, neck, and waist measurements (plus hips for women) to get your body fat percentage, fat mass, lean mass, and fitness category.
How does the body fat calculator work?
The US Navy method uses logarithmic formulas validated against hydrostatic weighing: for men, %BF = 495 ÷ (1.0324 − 0.19077×log10(waist−neck) + 0.15456×log10(height)) − 450. Accuracy is typically within ±3% of DEXA scan results when measurements are taken correctly.
Frequently Asked Questions
What is a healthy body fat percentage?
The American Council on Exercise classifies 14–24% as fit-to-average for men and 21–31% for women. Essential fat minimums are about 3% for men and 12% for women — going below is dangerous. Athletes typically sit at 6–13% (men) and 14–20% (women).
How accurate is the Navy tape method vs a DEXA scan?
Studies show the Navy circumference method lands within ±3–4% of DEXA for most people, which is comparable to consumer bioimpedance scales. Its biggest advantage is consistency — measuring the same way each month tracks your trend reliably even if the absolute number is slightly off.
Is the body fat calculator really free?
Yes — 100% free with no hidden charges, trial limits, or premium tiers for core features. You don't need to create an account or enter an email address. The site is supported by non-intrusive display ads, which keeps every tool free for everyone.
Is my data private when using the body fat calculator?
Completely. The body fat calculator runs entirely in your browser using JavaScript — nothing you type or upload is sent to our servers. When you close the tab, your data is gone. This makes it safe for confidential documents, financial figures, and personal information.
Does the body fat calculator work on mobile phones?
Yes. The body fat calculator is built mobile-first and works on any phone or tablet with a modern browser — iPhone (Safari), Android (Chrome), and everything in between. The layout adapts to small screens, so buttons and inputs stay easy to tap on a 375px-wide display.
Do I need to install anything to use the body fat calculator?
No. The body fat calculator works directly in your web browser — no downloads, no extensions, no signup. Just open the page, use the tool, and get your result instantly. It works on Windows, macOS, Linux, ChromeOS, iOS, and Android.