Temperature Converter
Convert between Celsius, Fahrenheit and Kelvin.
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About Temperature
Temperature is a small category with only three units, but it is one of the most used on the whole site because those three scales genuinely divide the world. Celsius is the everyday scale nearly everywhere and the one used in science alongside kelvin. Fahrenheit is the scale used for weather, cooking and body temperature in the United States. Kelvin is the SI base unit, the scale physicists and engineers use, and the one that appears on light bulb boxes to describe colour temperature. People land here for entirely practical reasons: reading a US weather forecast, setting an oven from an American recipe, checking whether a fever reading is high, or converting a thermodynamics figure for homework. The three pages that carry almost all of the traffic are Celsius to Fahrenheit, Fahrenheit to Celsius and Celsius to Kelvin.
Temperature has one property that makes it different from every other category here, and it is the source of most confusion. Length, weight and volume all convert by a simple ratio: double the input and you double the output. Temperature does not, because the scales have different zero points. Zero Celsius is the freezing point of water, zero Fahrenheit is somewhere else entirely, and zero kelvin is absolute zero, the point at which there is no thermal energy left at all. Because the starting lines are offset, converting requires a formula that both scales and shifts the number, not a single multiplication. That is why doubling a temperature in Celsius does not double it in Fahrenheit, why negative Fahrenheit values exist while negative kelvin values do not, and why you cannot convert a temperature by copying the trick you use for kilometers to miles. There is one useful exception: a difference of one kelvin is the same size as a difference of one degree Celsius, so a change in temperature converts more simply than a temperature itself.
Each of the pages here shows you the actual formula it applies rather than hiding it, walks through a worked example step by step, and gives you a reference table of the values people look up most, such as freezing point, body temperature and common oven settings. It is all free, no account is needed, and the conversion runs entirely in your browser so nothing you type is sent anywhere. If you are working on the energy side of heat rather than the temperature itself, the energy converter covers joules, calories and BTU.
Frequently asked questions
Why can I not just multiply to convert Celsius to Fahrenheit?
Because the two scales do not start at the same place. Zero Celsius is the freezing point of water, while zero Fahrenheit is a different temperature entirely. A conversion therefore has to both rescale the size of the degree and shift for that offset, which means a formula with an addition step, not a single ratio. This is the main way temperature differs from length or weight, where a plain multiplication is enough. The pair pages show the exact formula they use.
What is kelvin and why does it have no degree symbol?
Kelvin is the SI base unit of temperature and its zero is absolute zero, the coldest anything can theoretically be. Because it starts at a true zero rather than at an arbitrary reference point, it is written as a plain unit, so you say kelvin rather than degrees kelvin. It is used in science and engineering, and also to describe the colour of light sources. Its degree size matches Celsius, so a one kelvin change and a one degree Celsius change are the same amount.
Can a temperature be negative in every scale?
Celsius and Fahrenheit both go below zero freely, which is normal winter weather in much of the world. Kelvin does not: its zero is absolute zero, so a negative kelvin value has no physical meaning. If a conversion gives you a negative kelvin figure, the input was below absolute zero and is not a real temperature. That is a useful sanity check on any thermodynamics answer.
Do I need an account to use these converters?
No. All three temperature pages are free, need no sign-up and have no usage limit. The formula runs in your own browser, so the temperatures you enter are never uploaded. You can bookmark whichever direction you use most and it will load straight into that conversion.