Type into any box to convert between Celsius, Fahrenheit, Kelvin, and Rankine live, with the formula written out, a reference table, and a custom conversion chart.
| Celsius | – |
| Fahrenheit | – |
| Kelvin | – |
| Rankine | – |
| Nearest reference point | – |
| Description | °C | °F | K |
|---|
Click a row to load it into the converter. Oven equivalents follow the common British gas mark table; ovens vary by ±10 °C.
| °C | °F | K | °R |
|---|
This temperature converter links four scales, Celsius, Fahrenheit, Kelvin, and Rankine, so that typing into any one box updates the other three instantly. Beside the result it writes out the exact formula with your number substituted, which is what students, nurses, and cooks usually want to check, and it warns when a value falls below absolute zero, which no real temperature can. A reference table lists the landmarks people convert most: water freezing and boiling, normal body temperature and fever, room temperature, weather bands from freezing to extreme heat, and oven settings with British gas marks and their Fahrenheit equivalents; click any row to load it. A chart generator builds a conversion table over any range and step, for example every 5 °F from 300 to 500 for a recipe card or every degree from 35 to 42 °C for a fever chart, ready to copy or download as CSV. It is for travelers, cooks reading recipes from another country, students, and anyone who thinks in one scale but reads the other.
Temperature scales are affine, not proportional: they differ in both the size of a degree and the zero point, so conversion is a multiply and an add rather than a single factor. The definitions are exact. Celsius to Fahrenheit is °F = °C × 9/5 + 32 and back is °C = (°F − 32) × 5/9, because 100 Celsius degrees span 180 Fahrenheit degrees between the freezing and boiling points of water and the scales cross at −40. Kelvin has the same degree size as Celsius with its zero at absolute zero: K = °C + 273.15. Rankine is the absolute scale with Fahrenheit-sized degrees: °R = °F + 459.67, and K = °R × 5/9. Internally every value is converted to kelvin first and then to the target scale, so all four boxes always agree to floating-point precision, and results are rounded only for display at the number of decimal places you choose (2 by default, which turns 300 °F into 148.89 °C).
Double the Celsius value and add 30. That gives 70 for 20 °C (exact answer 68) and 90 for 30 °C (exact 86), close enough for weather. For a tighter estimate double it, subtract a tenth of that, and add 32: 20 °C → 40 − 4 + 32 = 68, which is exact. Going the other way, subtract 30 from the Fahrenheit value and halve it: 80 °F → 25 °C (exact 26.7). Remember the anchors −40 = −40, 0 °C = 32 °F, 10 °C = 50 °F, 20 °C = 68 °F, 30 °C = 86 °F, 37 °C = 98.6 °F, 100 °C = 212 °F.
Setting °C = °F in the conversion formula, x = x × 9/5 + 32, gives x − 9x/5 = 32, so −4x/5 = 32 and x = −40. The scales have different zero points (32 °F is 0 °C) and different degree sizes (a Fahrenheit degree is 5/9 of a Celsius degree), so their lines on a graph are not parallel and must cross exactly once, at −40. Kelvin and Celsius never meet because they have the same degree size and differ by a constant 273.15.
98.6 °F is simply 37 °C converted exactly, and 37 °C was a 19th-century average from Carl Wunderlich's measurements. Modern studies put the average adult oral temperature closer to 36.6 °C (97.9 °F), with a normal range of roughly 36.1 to 37.2 °C (97 to 99 °F) that varies by time of day, age, and where the temperature is taken. A fever is commonly defined as 38 °C (100.4 °F) or higher. Use this converter to translate a reading, but interpret it against those ranges rather than a single number.
Kelvin is the SI base unit of temperature and is used whenever a formula needs an absolute scale, one where zero means no thermal energy: gas laws, black-body radiation, color temperature of light (a 5,000 K bulb), and thermodynamics. Kelvin has no degree sign or word degree; it is just K. Rankine is the equivalent absolute scale built on Fahrenheit-sized degrees and appears mainly in older US engineering work, especially in aerospace and HVAC calculations that use imperial units. Neither scale can be negative, which is why this page flags any value that converts to below 0 K.
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