Formula and method
This calculator uses the values you enter and applies the calculation immediately in your browser. The main output formulas are:
- Estimated body fat:
(() => { if(waist<=neck) return NaN; const value=86.010*Math.log10(waist-neck)-70.041*Math.log10(height)+36.76; return value>=0 && value<=100 ? value : NaN; })()
Some formulas are undefined for certain input combinations, such as division by zero, equal x-values in a slope calculation, or logarithms of non-positive numbers. In those cases the live tool reports that the result is undefined instead of displaying Infinity or NaN.
Examples
- Example: with Waist = 34 in, Neck = 15 in, Height = 70 in, this calculator returns Estimated body fat = 17.5 %.
- Share this page with a clean URL: https://specwhale.com/tools/body-fat-calculator/
- Try related health & fitness tools when your next step needs another conversion or calculation.
How this compares to other estimation methods
This calculator uses a standard body fat estimation formula based on basic measurements. Circumference-based methods (like the Navy method) tend to track actual body fat somewhat more closely than BMI-based estimates because they account for body shape, but every non-lab method carries a real margin of error. See the body fat methods guide for a fuller comparison of what each approach can and can't tell you.
Embed this tool
Paste this snippet into your own site or blog post to embed a live, working copy of this tool. It links back to the full page on SpecWhale.
Frequently asked questions
Is Body Fat Calculator free to use?
Yes. Body Fat Calculator is completely free, has no usage limit, and does not require an account, email, or API key.
Does Body Fat Calculator store or upload my data?
No. Body Fat Calculator calculates everything locally in your browser. Nothing you type is sent to a server or stored by SpecWhale.
How accurate is Body Fat Calculator?
Body Fat Calculator uses a standard formula (see the Method section above for the exact expression). For high-stakes financial, medical, or legal decisions, confirm the result with a professional or an authoritative source before relying on it.
Can I embed Body Fat Calculator on my own website?
Yes. Use the "Embed this tool" snippet on this page to add a free, working copy of Body Fat Calculator to your own blog post or page.
SEO and sharing notes
This page has a single clean canonical URL, descriptive metadata, breadcrumb structured data, and internal links to related tools. Supported calculators and converters can also copy a prefilled share link without changing the canonical index URL.