Celsius to Fahrenheit Converter

The formula is °F = (°C × 9/5) + 32. Multiply the Celsius value by nine-fifths, then add 32 to the result. Celsius itself is formally defined through the Kelvin, the SI unit maintained by the International Bureau of Weights and Measures (BIPM).

The 9/5 factor exists because Celsius and Fahrenheit divide the same physical range into a different number of degrees. There are 100 degrees between freezing and boiling on the Celsius scale, but 180 degrees on the Fahrenheit scale. That ratio, 180 to 100, simplifies to 9/5.

Take the Celsius value, multiply it by 1.8, then add 32. Using 1.8 instead of the 9/5 fraction gives the identical result and is often faster to calculate by hand.

For example, 25°C multiplied by 1.8 equals 45. Adding 32 to that gives 77°F, which is the correct converted value.

For a fast approximation without a calculator, double the Celsius value and add 30. This shortcut is close enough for everyday use, though it is not exact.

Applied to 20°C, doubling gives 40, and adding 30 gives 70°F. The precise formula gives 68°F, so the trick is off by only 2 degrees. That margin holds fairly steady across normal outdoor temperatures. It is why the trick works well for weather but not for lab or medical readings.

These five examples cover the values people look up most often, from everyday weather to cooking and cold-weather extremes.

Each of these follows directly from the formula above and can be used to double-check your own calculations.

Fahrenheit is the everyday scale in the United States, its territories, and a small number of other countries. It appears on weather reports, oven dials, and most home thermostats. Celsius is the standard almost everywhere else, including the entire scientific and medical community worldwide.

This split means the same recipe, weather forecast, or lab reading can arrive in either unit depending on its source. Travelers, cooks following international recipes, and anyone reading foreign news coverage run into this conversion more often than they expect.

Developers who need this conversion in their own project can use the function below instead of re-deriving the formula. It matches exactly what powers the calculator on this page.

function celsiusToFahrenheit(celsius) {
  return (celsius * 9 / 5) + 32;
}

Copy the snippet directly into a JavaScript project. No dependencies are required, and the same formula applies in any programming language.

This converter runs entirely in your browser using client-side JavaScript. The value you enter is never transmitted to our servers or stored anywhere outside your current session.

You can confirm this yourself by disconnecting your internet connection after the page loads. The tool keeps working normally, since no network request is involved in producing a result.

These are the most frequent errors people make with this conversion, along with the fix for each.

The table below lines up common reference points in both scales for quick lookup.

Need Kelvin instead? Our dedicated Kelvin Converter covers all four Celsius, Fahrenheit, and Kelvin direction pairs in one place. Going the other direction? See our Fahrenheit to Celsius converter for that formula and its own shortcut. For a single tool covering all three scales, see our full Temperature Converter.