A weather forecast in Fahrenheit, an oven setting in Celsius, a lab reading in kelvin — the same heat, three different numbers. This free temperature converter switches between Celsius, Fahrenheit and kelvin with the exact formulas, so 25 °C reads as 77 °F and 298.15 K without any mental arithmetic. Everything runs in your browser, so nothing is uploaded and no signup is needed.
How to use this temperature converter
Three quick steps — value, scale, result.
Type the reading you have, including a minus sign for below-zero values.
Pick Celsius, Fahrenheit or kelvin as the starting scale.
The other two scales appear at once, so a forecast, a recipe or a lab value is checked in one glance.
Why this temperature converter gets the offsets right
Built to be free, private, and exact — right in your browser.
Scales differ in where zero sits and in how big a degree is, so the tool applies both the offset and the 9/5 factor — never just one.
Kelvin takes no degree symbol: it is 298.15 K, not 298.15 °K, and it never goes below zero.
Minus 40 is the one temperature where Celsius and Fahrenheit agree, which is a useful check that a conversion has not gone wrong.
The conversion itself is exact, but it converts a reading, not a weather forecast or a sensor calibration — it cannot know how accurate your thermometer was.
A reading is not a temperature change
The mistake almost every temperature guide leaves out.
Converting a reading needs the offset; converting a change must not use it. A day that warms from 20 °C to 30 °C has risen by 10 Celsius degrees, which is 18 Fahrenheit degrees — not 50 °F, which is what you get if you wrongly convert 10 °C as a reading.
The same applies to kelvin. A rise of 10 Celsius degrees is a rise of 10 kelvin, because the two scales share the same degree size and differ only in where zero sits.
So check what your number is. If it is a thermometer reading, use the full formula with its offset. If it is a difference — a warming, a cooling, a tolerance — multiply by 9/5 or 5/9 only.
Temperature Converter FAQs
Short, direct answers to the questions readers ask most.
Multiply by 9/5 and add 32: 25 °C × 9/5 + 32 = 77 °F.
It adds 273.15 to a Celsius reading, so 25 °C becomes 298.15 K; to go back, subtract 273.15.
Absolute zero: 0 K, which is −273.15 °C or −459.67 °F. Anything below that is rejected as physically impossible for an ordinary reading.
Because of the 32 offset. A reading and a temperature change convert differently: a rise of 10 Celsius degrees is a rise of 18 Fahrenheit degrees, with no offset involved.
Yes for the arithmetic, with one caution: the tool converts the number you set, not what your oven actually reaches, which depends on the appliance.
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