Temperature Converter

Convert temperatures between Celsius, Fahrenheit and Kelvin, with the exact formula for each pair and a worked example using your own value.

Value

From

–

Formula:

Significant figures

≈ means the result was rounded to the chosen number of significant figures.

{value} in every unit

Unit	Result

Quick conversion table: {from} to {to}

From	To

Common values

Reference	Value	Result

Formula

Unit	Formula

How to use the temperature converter

Type a temperature in Value. Negative values and decimals are fine (−12.5 or −12,5).
Choose the scale you start from in From and the scale you want in To.
Read the result as you type. Under it, Formula shows the formula for the selected pair, and the next line applies it to your value step by step.
Press the Swap units button (⇄) to convert the other way, for example from °F back to °C.
Change Significant figures for more or fewer digits, and use Copy to copy the full line, such as “20 °C = 68 °F”.

Further down, the tool lists your temperature on all three scales, a quick conversion table (from −40 to 180 °C expressed in your starting scale), everyday reference temperatures, and the formulas from your starting scale to each of the others.

The formulas

Temperature scales do not share the same zero, so converting is not a simple multiplication: there is a factor and an offset.

Celsius to Fahrenheit: °F = °C × 1.8 + 32 (1.8 is 9/5)
Fahrenheit to Celsius: °C = (°F − 32) × 5/9
Celsius to Kelvin: K = °C + 273.15
Kelvin to Celsius: °C = K − 273.15
Fahrenheit to Kelvin: K = (°F + 459.67) × 5/9
Kelvin to Fahrenheit: °F = K × 1.8 − 459.67

The factor 9/5 comes from the size of the degrees: between the freezing and boiling points of water there are 100 Celsius degrees but 180 Fahrenheit degrees. A kelvin is exactly the same size as a Celsius degree; only the starting point differs.

Worked example

A fever thermometer reads 101.3 °F. Using the second formula: (101.3 − 32) × 5/9 = 69.3 × 5/9 = 38.5 °C. The tool shows the same calculation under Formula, with your own numbers.

Why temperature differences are different

The formulas above convert a temperature reading. A temperature difference converts without the offset: a rise of 10 °C is a rise of 18 °F, not 50 °F. So if a recipe says “lower the oven by 20 °C”, that is 36 °F lower. Kelvin and Celsius differences are identical.

Absolute zero

0 K (−273.15 °C, −459.67 °F) is absolute zero, the lowest possible temperature. The Kelvin scale starts there, which is why it has no negative values and why scientists use it. If you enter a value below absolute zero, the tool still shows the arithmetic but warns you that such a temperature cannot exist.

Handy reference points

−40 °C = −40 °F: the only temperature where both scales agree.
0 °C = 32 °F = 273.15 K: water freezes.
20 °C = 68 °F: comfortable room temperature.
37 °C = 98.6 °F: normal body temperature.
100 °C = 212 °F: water boils at sea level.
180 °C ≈ 356 °F: a moderate oven, often rounded to 350 °F in recipes.

Frequently asked questions

How do I convert Celsius to Fahrenheit in my head?

Double the Celsius value and add 30. For 20 °C that gives 70 °F instead of the exact 68 °F. The approximation is good near room temperature and gets worse at extremes.

Is it "degrees Kelvin"?

No. Since 1967 the unit is simply the kelvin, symbol K, with no degree sign: 300 K, not 300 °K.

At what temperature are Celsius and Fahrenheit equal?

At −40. Solving °F = °C × 1.8 + 32 with °F = °C gives −0.8 × °C = 32, so °C = −40.

Why does the result sometimes start with "≈"?

Fahrenheit to Celsius involves dividing by 9, which often gives an endless decimal (100 °F = 37.777… °C). The result is rounded to the chosen Significant figures and marked with “≈”.

Where do the Fahrenheit numbers come from?

Daniel Gabriel Fahrenheit set his scale in the early 18th century from reference points such as a brine mixture and body temperature. Today it is defined from the kelvin through the formulas above.