Temperature Converter
Celsius · Fahrenheit · Kelvin · Rankine
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Temperature Reference Points
To convert Celsius to Fahrenheit, multiply by 1.8 and add 32; to go back, subtract 32 and divide by 1.8. So 20 °C is 68 °F and 100 °F is 37.8 °C. Kelvin is Celsius plus 273.15. Pick a scale above, type a temperature, and you get all four scales along with the formula used for each.
Key temperatures everyone should know, shown in all four scales.
| Reference Point | °C | °F | K |
|---|---|---|---|
| Absolute Zero | −273.15 | −459.67 | 0 |
| Water Freezes | 0 | 32 | 273.15 |
| Room Temp | 20 | 68 | 293.15 |
| Body Temp | 37 | 98.6 | 310.15 |
| Water Boils | 100 | 212 | 373.15 |
| Oven (moderate) | 180 | 356 | 453.15 |
The Celsius and Fahrenheit scales cross at −40°, the only temperature that is the same in both. Kelvin starts at absolute zero and has no negative values. Rankine is the imperial equivalent of Kelvin.
Celsius and Fahrenheit Conversion Table
Fahrenheit values from Celsius are exact; Celsius values from Fahrenheit are rounded to one decimal.
| °C | °F | °F | °C |
|---|---|---|---|
| −40 | −40 | −40 | −40 |
| −30 | −22 | −20 | −28.9 |
| −20 | −4 | 0 | −17.8 |
| −10 | 14 | 10 | −12.2 |
| 0 | 32 | 20 | −6.7 |
| 5 | 41 | 32 | 0 |
| 10 | 50 | 40 | 4.4 |
| 15 | 59 | 50 | 10 |
| 20 | 68 | 60 | 15.6 |
| 25 | 77 | 70 | 21.1 |
| 30 | 86 | 80 | 26.7 |
| 35 | 95 | 90 | 32.2 |
| 37 | 98.6 | 98.6 | 37 |
| 40 | 104 | 100 | 37.8 |
| 100 | 212 | 212 | 100 |
Oven Temperatures in Fahrenheit and Celsius
Recipes rarely use the exact conversion. The usual rounded Celsius settings and UK gas marks are shown next to the exact value.
| °F | Exact °C | Usual recipe °C | Gas mark |
|---|---|---|---|
| 250 | 121.1 | 120 | 1/2 |
| 275 | 135.0 | 140 | 1 |
| 300 | 148.9 | 150 | 2 |
| 325 | 162.8 | 170 | 3 |
| 350 | 176.7 | 180 | 4 |
| 375 | 190.6 | 190 | 5 |
| 400 | 204.4 | 200 | 6 |
| 425 | 218.3 | 220 | 7 |
| 450 | 232.2 | 230 | 8 |
| 475 | 246.1 | 240 | 9 |
For a fan (convection) oven, recipes usually lower the setting by about 20 °C, or 25 °F.
Temperature Differences Work Differently
A change in temperature converts without the 32. A rise of 10 °C is a rise of 18 °F, because only the size of the degree matters: 1 °C = 1.8 °F = 1 K = 1.8 °R. If the forecast says it will be 5 °C cooler tomorrow, that is 9 °F cooler, not 41 °F.
Common mistakes
- Adding 32 to a difference. Only actual temperatures get the offset. Differences use the 1.8 factor alone.
- Using 273 instead of 273.15. It is off by 0.15 K. That is fine for a rough answer, not for lab or engineering work.
- Trusting "double it and add 30" everywhere. The shortcut is exact at 10 °C (50 °F), 4 °F too high at 30 °C (90 against 86) and 18 °F too high at 100 °C (230 against 212).
- Writing "degrees Kelvin". The unit is the kelvin, symbol K, with no degree sign: water boils at 373.15 K.
Method and sources. Formulas from NIST Special Publication 811 (sections 4.2.1.1 and B.8): T(K) = t(°C) + 273.15, t(°F) = 1.8 × t(°C) + 32 and T(°R) = t(°F) + 459.67 = 1.8 × T(K), all exact. Since 2019 the kelvin is defined by fixing the Boltzmann constant at 1.380649 × 10−23 J/K (BIPM SI Brochure, 9th edition). The table values were computed with the same formulas as the converter. Recipe settings and gas marks are conventional roundings, not exact conversions.
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Temperature Questions
Multiply the Celsius value by 9/5 (or 1.8) and add 32. Formula: °F = (°C × 9/5) + 32. Example: 100°C = (100 × 1.8) + 32 = 212°F. To convert the other way: °C = (°F − 32) × 5/9. Example: 98.6°F = (98.6 − 32) × 5/9 = 37°C.
Simply add 273.15. Formula: K = °C + 273.15. The Kelvin scale has the same interval size as Celsius: a change of 1°C is a change of 1 K. The only difference is the starting point: 0 K is absolute zero (−273.15°C). Water freezes at 273.15 K and boils at 373.15 K.
The Celsius and Fahrenheit scales cross at exactly −40°. At −40, both scales give the same number: −40°C = −40°F. This is because the formula °F = (°C × 1.8) + 32 has a solution at −40. Below −40, the Fahrenheit value is lower; above −40, the Fahrenheit value is higher than the Celsius value.
Absolute zero is the coldest possible temperature, the point at which matter has the least thermal energy it can have. It is defined as 0 Kelvin = −273.15°C = −459.67°F = 0°R. It cannot be reached in practice, although laboratories have cooled matter to within a billionth of a kelvin of it. The Kelvin and Rankine scales both start at absolute zero, which is why they have no negative values.
The commonly cited value is 37°C (98.6°F), based on measurements published by Carl Wunderlich in 1868. Modern studies suggest the average is slightly lower at 36.6°C (97.9°F), and varies by time of day, age and measurement location. A fever is typically defined as 38°C (100.4°F) or above. The normal range is roughly 36.1 to 37.2°C (97 to 99°F).
Both Kelvin and Rankine start at absolute zero, making them absolute temperature scales. The difference is the size of the degree interval. Kelvin uses the same interval as Celsius (metric system), while Rankine uses the same interval as Fahrenheit (imperial system). So 1 K = 1.8°R. Rankine is mostly used in some US engineering fields. Conversion: °R = K × 1.8 = °F + 459.67.
The Fahrenheit scale was established in 1724 by Daniel Fahrenheit and adopted widely before the metric system was standardized. The US, along with a few places such as the Bahamas, Belize and the Cayman Islands, still uses Fahrenheit for everyday temperatures. The UK officially adopted Celsius in the 1960s-70s but still uses Fahrenheit colloquially for weather. The Celsius scale, proposed in 1742 by Anders Celsius, is used almost everywhere else and in science worldwide.
At standard atmospheric pressure (1 atm = 101.325 kPa), water freezes at 0°C (32°F, 273.15 K) and boils at 100°C (212°F, 373.15 K). These were actually the original definition of the Celsius scale. At higher altitudes the boiling point drops (e.g. water boils at ~90°C at 3,000 m elevation). At higher pressures the boiling point rises: this is why pressure cookers cook faster.
37°C = 98.6°F. This is the standard human body temperature. Calculation: (37 × 9/5) + 32 = 66.6 + 32 = 98.6. Other useful medical temperatures: 36°C = 96.8°F, 38°C = 100.4°F (fever threshold), 39°C = 102.2°F, 40°C = 104°F (high fever). Use this converter to check any temperature quickly.
180°C = 356°F, which rounds to 350°F in most recipes: a moderate oven. Other common oven conversions: 160°C = 320°F (slow/low) · 200°C = 392°F (hot) · 220°C = 428°F (very hot) · 250°C = 482°F (extremely hot). UK recipes often use Gas Mark: 180°C = Gas Mark 4. Fan ovens typically run 20°C lower than conventional ovens.
350 °F is 176.7 °C: (350 − 32) × 5/9 = 176.67. Recipes round it to 180 °C, which is Gas Mark 4, or use about 160 °C in a fan oven.
0 °F is −17.8 °C (exactly −160/9). Daniel Fahrenheit set the zero of his scale at the coldest temperature he could reliably make with a mixture of ice, water and a salt.
Multiply by 1.8 and do not add 32. A rise of 10 °C is a rise of 18 °F, and a drop of 3 °F is a drop of 1.67 °C. The 32 only shifts the starting point of the scale, so it cancels out when you subtract one temperature from another.