Type a whole phrase like 12 ft to m in the bar at the top, or pick a category and units below. Conversions run at full precision internally and round only for display. Click any cell in the unit grid to make it the “to” unit; star a pair you use often to pin it above the converter.
Converting 100°F to Celsius isn't a simple multiply — temperature scales have an offset as well as a ratio. This tool applies the exact affine formula (°C = (°F − 32) × 5/9), so the result — 37.8°C — matches a lab thermometer, not just a mental-math shortcut.
Where a factor is defined by international standard — the inch, the pound, the international foot — it's used to full precision, not rounded early. A few less common units use the best publicly available conversion factor, clearly no less precise than typical reference tables.
Because real-world unit choice is messy: cooking uses cups and teaspoons, engineering uses pascals and psi, shipping uses different “tons” depending on the country. The category list reflects units people actually encounter, not just the metric/imperial pair.
No — categories are kept separate because there's no general conversion between fundamentally different physical quantities. Density is its own category because mass/volume is a defined physical quantity with standard units — not an arbitrary cross-category multiply.
No — they're official European Central Bank reference rates, published once per working day around 16:00 CET. They're not intraday trading prices, so don't use this for anything time-sensitive.
Every other category converts using a fixed physical constant. Exchange rates change daily, so there's no fixed factor to bake in; this is the only place this tool talks to an external service (Frankfurter / ECB), and the request goes from your browser — nothing passes through this site's servers.
This page has changed in 46 archived releases, but each of those was a site-wide pass, so none is attributable to this tool on its own and none is listed here. That is not a claim that the tool never changed — a release that reworked many pages at once may well have altered this one too. The changelog has them.