Temperature Converter
Convert between Celsius, Fahrenheit, Kelvin and Rankine. Free, and runs entirely in your browser — nothing you enter is uploaded or stored.
About Temperature Converter
Converts a temperature between Celsius, Fahrenheit, Kelvin and Rankine, and shows all four at once so you never have to pick the target first. Type a reading in any scale and every other row updates from it.
Celsius and Fahrenheit differ in both where they start and how big a degree is, which is why the conversion is not a single multiplication: water freezes at 0 °C and 32 °F, and a Celsius degree is 1.8 Fahrenheit degrees. Kelvin and Rankine start at absolute zero, the coldest anything can be, so they have no negative values — the converter refuses a reading below it rather than giving a physically impossible answer.
Where it helps
- All four scales from one reading, with no target to choose first.
- Exact formulas, not rounded rules of thumb such as doubling and adding thirty.
- Refuses temperatures below absolute zero instead of printing an impossible number.
- Takes decimals and negative readings, which a winter forecast needs.
Limits
- It converts a reading; it cannot convert a temperature difference, where 10 °C of change is 18 °F rather than 50 °F.
- Rarely used scales such as Réaumur and Delisle are left out.
- Results carry ten significant figures, more than any thermometer can measure, so round them for everyday use.
Frequently asked questions
How do I convert Celsius to Fahrenheit in my head?
Double it and add 30 gets you close for weather temperatures. The exact rule is multiply by 1.8 and add 32, which is what this converter uses.
Where do Celsius and Fahrenheit meet?
At −40, where both scales read the same number. Enter −40 in either and the other row shows −40 as well.
Why is there no negative Kelvin?
Kelvin starts at absolute zero, the point where particles have the least energy they can. Nothing can be colder, so the scale has nowhere below zero to go.
What is Rankine used for?
It is the absolute scale with Fahrenheit-sized degrees, still found in some American engineering and thermodynamics work, just as Kelvin is the absolute scale with Celsius-sized degrees.
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