Nothing. The converter is a single web page that runs entirely on your device. It has no login, no database, and no back-end that receives anything you type.
The amount and unit you enter are converted in your browser, and your last category, unit, precision setting and entry are auto-saved in your browser's localStorage on that one device so the page opens where you left off. If you click "Download this tool," a file is saved to your own computer. In both cases the data never leaves your machine — we cannot see it, and there is no way for us to.
To erase locally saved data, clear this site's storage in your browser settings.
This site uses Cloudflare Web Analytics, a privacy-first, cookieless measurement tool, to count visits and see which referring sites are popular. It sets no cookies, does not track you across other websites, and does not fingerprint your device or collect any personal data — it records only aggregate, anonymous page-view counts. There are no advertising scripts and no other third-party trackers. (Offline copies saved with "Download this tool" have the analytics script removed entirely and make no network calls at all.)
What you convert is never measured or transmitted. The analytics beacon only knows that a page was viewed — never anything you type.
Every conversion factor is built into the page itself. The converter does not look anything up online, so typing in it produces zero network requests. You can verify this yourself: open your browser's developer tools, switch to the Network tab, and convert away — nothing will appear. Or turn off Wi-Fi entirely; the page keeps working.
The page links to a few outside sites (for example, the sibling calculators and the Ko-fi support page). Those are plain links that open in a new tab — this tool never sends anything to them. What you do on those sites is governed by their own privacy policies.
The page is served as a static file by Cloudflare Workers. As with any website, Cloudflare may log standard, server-side request metadata (such as IP address and timestamp) for security and reliability, governed by Cloudflare's own privacy policy. This application stores no user data server-side.
If this policy changes, the "Last updated" date above will reflect it. Since no personal data is collected, changes are unlikely to affect you.