Tinker 
How to use the temperature converter
Enter the temperature you have, pick the unit it is in, and choose the unit you want. The highlighted result shows the conversion you asked for, and the list underneath shows the same temperature in all four scales, so you never need to run it twice.
Negative numbers work for all scales except Kelvin and Rankine, which start at absolute zero. If you type something colder than absolute zero, the converter tells you instead of producing a meaningless number.
The formulas in words
Celsius to Fahrenheit: multiply by 9/5 (that is 1.8) and add 32. Fahrenheit to Celsius: subtract 32, then multiply by 5/9.
Celsius to Kelvin: add 273.15. Kelvin uses the same size of degree as Celsius but starts at absolute zero, so there are no negative Kelvin temperatures and no degree sign.
Fahrenheit to Rankine: add 459.67. Rankine is to Fahrenheit what Kelvin is to Celsius, and it still appears in some American engineering and thermodynamics work.
Behind the scenes, the converter turns your value into Celsius first and then calculates every other scale from that, rounding each answer to two decimals.
Worked example: a 25 °C summer day
Fahrenheit: 25 × 1.8 = 45, and 45 + 32 = 77 °F.
Kelvin: 25 + 273.15 = 298.15 K.
Rankine: 77 + 459.67 = 536.67 °R.
Going the other way, a body temperature of 98.6 °F becomes (98.6 − 32) × 5/9 = 66.6 × 5/9 = 37 °C, which is 310.15 K.
Handy reference points and tips
Water freezes at 0 °C (32 °F, 273.15 K) and boils at 100 °C (212 °F, 373.15 K) at sea level. Room temperature is roughly 20–22 °C (68–72 °F). A moderate oven at 180 °C is 356 °F, usually rounded to 350 °F in recipes.
For a quick mental estimate from Celsius to Fahrenheit, double the number and add 30. It is close for everyday weather but drifts at extremes, so use the exact result for cooking, science or medicine.
At −40 the Celsius and Fahrenheit scales meet: −40 °C is exactly −40 °F.
Frequently asked questions
How do I convert Celsius to Fahrenheit?
Multiply the Celsius value by 1.8 and add 32. For example, 30 °C × 1.8 = 54, plus 32 gives 86 °F.
Why is there no degree symbol for Kelvin?
Kelvin is an absolute scale defined from absolute zero, so values are written simply as kelvins, for example 300 K, not 300 °K. The degree symbol was officially dropped in 1967.
At what temperature are Celsius and Fahrenheit equal?
At −40. Solving C = C × 1.8 + 32 gives C = −40, so −40 °C and −40 °F are the same temperature.
Can a temperature be below 0 Kelvin?
No. 0 K (−273.15 °C or −459.67 °F) is absolute zero, the lowest possible temperature, so the converter rejects anything colder.