Temperature Converter guide
Type a temperature, pick Fahrenheit, Celsius, or Kelvin, and see the other two instantly. Useful for oven settings, weather abroad, fevers, and science homework.
Enter once, read three answers
Type a number, choose whether it is Fahrenheit, Celsius, or Kelvin, and the converter shows the value in all three scales at the same time. No swapping dropdowns back and forth. If you enter something colder than absolute zero, like -500 F, the tool flags it, because no real temperature can go there.
The exact formulas
Celsius to Fahrenheit: F = C x 9/5 + 32. Fahrenheit to Celsius: C = (F - 32) x 5/9. Celsius to Kelvin: K = C + 273.15. Fahrenheit to Kelvin goes through Celsius first: K = (F - 32) x 5/9 + 273.15.
Why 9/5? Water freezes at 0 C and 32 F and boils at 100 C and 212 F at sea level. That is 100 Celsius degrees spanning 180 Fahrenheit degrees, a ratio of 1.8, or 9/5. The +32 shifts the zero point. Kelvin uses Celsius-sized degrees but starts at absolute zero, so it is just an offset of 273.15.
Kelvin is written without a degree sign: 300 K, not 300 degrees K. Room temperature, 75 F, is 23.9 C or about 297 K.
Worked examples
Fever check: a thermometer reads 38.5 C. Multiply by 1.8 to get 69.3, add 32, and you get 101.3 F. A fever is generally defined as 100.4 F (38 C) or higher.
Weather abroad: the forecast in Madrid says 30 C. 30 x 1.8 + 32 = 86 F. Warm, not scorching. 40 C, which southern Spain does hit in summer, is 104 F.
Chemistry lab: a gas is at 300 K. Subtract 273.15 to get 26.85 C, then 26.85 x 1.8 + 32 = 80.33 F.
Kitchen temperatures Americans actually need
Ovens: 325 F is 162.8 C, 350 F is 176.7 C, 375 F is 190.6 C, 400 F is 204.4 C, and 425 F is 218.3 C. European recipes usually round to the nearest 10, so you will see 180 C for 350 F and 200 C for 400 F. Fan (convection) ovens often run about 20 C lower than conventional settings in UK recipes, so check which one the recipe assumes.
Food safety, from USDA minimum internal temperatures: poultry 165 F (73.9 C), ground beef and pork 160 F (71.1 C), whole cuts of beef, pork, and lamb 145 F (62.8 C) with a 3-minute rest. Keep your refrigerator at 40 F (4.4 C) or below and your freezer at 0 F (-17.8 C).
Quick mental math, and where it breaks
Celsius to Fahrenheit in your head: double it and add 30. 20 C becomes 70 F; the exact answer is 68. Fahrenheit to Celsius: subtract 30 and halve. 80 F becomes 25 C; exact is 26.7.
The shortcut is close near room temperature and drifts badly at the extremes. At 100 C it gives 230 F instead of 212, an 18-degree miss. Fine for deciding on a jacket. Not fine for candy making or a lab report. Use the exact number for anything that matters.
Another trap: temperature differences convert without the 32. A 10 C rise is an 18 F rise, not 50 F. Only absolute readings use the offset.
Why the US still uses Fahrenheit
Daniel Gabriel Fahrenheit proposed his scale in the 1720s, and it spread through the British Empire. Anders Celsius published his in 1742; oddly, his original version had water boiling at 0 and freezing at 100, and it was flipped shortly after. Most of the world switched to Celsius during metrication in the 20th century. The US did not, so everyday weather, cooking, and medicine stay in Fahrenheit, while US science and engineering work in Celsius and Kelvin.
One argument for Fahrenheit: it has finer steps for weather, and 0 to 100 F roughly covers the outdoor range many Americans experience. One argument against: water's key points land on 32 and 212. Either way, you now have both.
How we calculate: sources
Frequently asked questions
How do I convert Fahrenheit to Celsius?
Subtract 32, then multiply by 5/9. 68 F is (68 - 32) x 5/9 = 20 C.
How do I convert Celsius to Fahrenheit?
Multiply by 9/5 (1.8), then add 32. 25 C is 25 x 1.8 + 32 = 77 F.
What is 350 F in Celsius?
176.7 C, which most European ovens and recipes round to 180 C. 400 F is 204.4 C, usually written as 200 C.
What is normal body temperature in Celsius?
The classic figure is 98.6 F, which is exactly 37 C. Normal readings vary by person and time of day, and a fever is generally considered 100.4 F (38 C) or higher.
At what temperature are Fahrenheit and Celsius equal?
-40. At -40 degrees, both scales read the same number.
What is absolute zero?
The lowest possible temperature: 0 K, -273.15 C, or -459.67 F. The converter flags any value below it as physically impossible.
Is my data kept private?
Everything runs in your browser. Nothing you enter is uploaded to a server or stored by us.
Can Kelvin be negative?
No. 0 K is absolute zero, the coldest anything can be, so every real temperature in Kelvin is zero or positive.
What temperature does water boil at in Fahrenheit?
212 F at sea level. It boils at lower temperatures at altitude, which is why high-altitude baking instructions exist.