Temperature is the one category where converting is not simply scaling. The scales have different zeros, so every conversion shifts as well as stretches, and a difference of one degree does not convert the same way a temperature of one degree does. These tools convert directly between the two scales you asked for instead of routing through kelvin, which would quietly lose precision around freezing point.
Tools in this category
Kelvin to Celsius
Convert kelvin to Celsius with the exact relation NIST publishes. The degrees are the same size, so subtracting 273.15 is the whole conversion.
Fahrenheit to Kelvin
Convert Fahrenheit to kelvin in one step. Kelvin has no degree sign and no negative values, because it starts at absolute zero.
Celsius to Kelvin
Convert Celsius to Kelvin in your browser. The two scales share a degree size, so only the zero point moves.
Celsius to Fahrenheit
Convert Celsius to Fahrenheit in your browser. Temperature is an offset scale, not a simple multiple, so 0 °C is 32 °F rather than zero.
Fahrenheit to Celsius
Convert Fahrenheit to Celsius using the exact relation published by NIST, computed in your browser with no detour through kelvin.
Suggest a tool
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What should it convert, calculate or generate, and where would the authoritative numbers come from? A link to the standard or publication that defines them is the most useful thing you can send.
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How these tools are built
Every tool in this category runs entirely in your browser: there is no upload, no account and no request to a server once the page has loaded. The numbers behind them are transcribed from the organisation that defines them — NIST for units, the W3C for web formats, the WHO for health measures — and each page names its source next to the formula. A tool whose reference values stop reproducing fails the build and does not ship, which is the whole reason the catalogue grows slowly.