Temperature Converter
Convert between Celsius, Fahrenheit and Kelvin instantly.
Convert Celsius, Fahrenheit and Kelvin
This temperature converter switches instantly between the three main temperature scales: Celsius (°C), used in most of the world; Fahrenheit (°F), used in the United States; and Kelvin (K), the scientific standard. Type a temperature, choose your scales, and the result appears immediately — handy for cooking, weather, travel between the US and UK, and science.
The conversion formulas
To convert Celsius to Fahrenheit, multiply by 9/5 and add 32 (°F = °C × 9/5 + 32). To go from Fahrenheit to Celsius, subtract 32 and multiply by 5/9. Kelvin shares the size of a Celsius degree but starts at absolute zero, so K = °C + 273.15. The calculator applies the correct formula automatically for whatever scales you select.
Common temperature reference points
| Description | Celsius | Fahrenheit |
|---|---|---|
| Water freezes | 0 °C | 32 °F |
| Room temperature | 20 °C | 68 °F |
| Body temperature | 37 °C | 98.6 °F |
| Water boils | 100 °C | 212 °F |
Frequently asked questions
What is 100°F in Celsius?
100°F is about 37.8°C — close to normal body temperature. Subtract 32 and multiply by 5/9 to convert any Fahrenheit value.
Why do scientists use Kelvin?
Kelvin starts at absolute zero, the coldest possible temperature, so it has no negative values. This makes it ideal for physics and chemistry calculations, especially gas-law problems where temperatures must be multiplied or divided.
At what temperature are Celsius and Fahrenheit equal?
At −40. Minus 40 °C is exactly minus 40 °F, the only point where the two scales meet. You can check it with the formula: −40 × 9/5 + 32 = −72 + 32 = −40.
What is absolute zero?
Absolute zero is 0 K, which equals −273.15 °C or −459.67 °F. It is the lowest temperature physically possible, where particles have the minimum energy allowed by quantum mechanics.
Worked examples
Celsius to Fahrenheit: a summer day
- Start with 25 °C.
- Multiply by 9/5 (or 1.8): 25 × 1.8 = 45.
- Add 32: 45 + 32 = 77 °F.
Fahrenheit to Celsius: a US oven setting
- Start with 350 °F.
- Subtract 32: 350 − 32 = 318.
- Multiply by 5/9: 318 × 5 ÷ 9 = 176.7 °C.
UK recipes usually round this to 180 °C, or 160 °C in a fan oven, because fan ovens cook roughly 20 degrees hotter.
Kelvin to Celsius and Fahrenheit
A lab sample is at 300 K. Subtract 273.15 to get 26.85 °C, then apply the Fahrenheit formula: 26.85 × 1.8 + 32 = 80.33 °F.
Converting a temperature change, not a temperature
A common mistake is to add 32 when converting a difference in temperature. If a weather forecast says it will be 10 °C warmer tomorrow, that is a rise of 18 °F, not 50 °F. For differences, only multiply by 1.8 (Celsius to Fahrenheit) or divide by 1.8 (Fahrenheit to Celsius). A change of 1 °C is always the same as a change of 1 K.
Oven temperature and gas mark chart
British recipes often use gas marks. The table gives the usual conventional-oven equivalents; manufacturers vary slightly, so treat these as a guide.
| Gas mark | Celsius | Fan oven | Fahrenheit |
|---|---|---|---|
| 1 | 140 °C | 120 °C | 275 °F |
| 2 | 150 °C | 130 °C | 300 °F |
| 3 | 170 °C | 150 °C | 325 °F |
| 4 | 180 °C | 160 °C | 350 °F |
| 5 | 190 °C | 170 °C | 375 °F |
| 6 | 200 °C | 180 °C | 400 °F |
| 7 | 220 °C | 200 °C | 425 °F |
| 8 | 230 °C | 210 °C | 450 °F |
| 9 | 240 °C | 220 °C | 475 °F |
Quick mental shortcut
For weather temperatures, double the Celsius figure and add 30 to estimate Fahrenheit. 15 °C becomes about 60 °F (exact 59 °F). To go back, subtract 30 and halve: 80 °F is about 25 °C (exact 26.7 °C). The shortcut drifts at extremes, so use the converter above for cooking, medicine or science.
A short history of the three scales
Daniel Gabriel Fahrenheit proposed his scale in 1724, and it spread through the British Empire and America. Anders Celsius introduced a 100-step scale in 1742 based on the freezing and boiling points of water. Lord Kelvin described an absolute scale in 1848, starting from the coldest possible temperature. Since 2019, the kelvin has been defined through the Boltzmann constant, and the Celsius and Fahrenheit scales are both defined from the kelvin. Today almost every country uses Celsius for weather, while the United States still uses Fahrenheit for everyday purposes.
For other conversions, try the energy converter, the cooking measurement converter or the all-in-one unit converter.