Fahrenheit and Celsius are the scales most often used for reporting room, weather, and water temperatures. The Fahrenheit scale is used in the United States, while the Celsius scale is used worldwide.

Indeed, most countries around the world measure their weather and temperatures using the relatively simple Celsius scale. But the United States is one of just a few remaining countries that use Fahrenheit, so it's important for Americans to know how to convert one to the other, especially when traveling or doing scientific research.

How to Convert Temperatures

First, you need the formula for converting Fahrenheit (F) to Celsius (C):

C = 5/9 x (F-32)

The notation C represents the temperature in Celsius, and F is the temperature in Fahrenheit. After you know the formula, it is easy to convert Fahrenheit to Celsius with these three steps.

Subtract 32 from the Fahrenheit temperature. Multiply this number by five. Divide the result by nine.

For example, suppose the temperature is 80 degrees Fahrenheit and you want to know what the figure would be in Celsius. Use the above three steps:

80 F – 32 = 48 5 x 48 = 240 240 / 9 = 26.7 C

So the temperature in Celsius is 26.7 C.

Fahrenheit to Celsius Example

If you want to convert a normal human body temperature (98.6 F) to Celsius, plug the Fahrenheit temperature into the formula:

C = 5/9 x (F - 32)

As noted, your starting temperature is 98.6 F. So you would have:

C = 5/9 x (F - 32)

C = 5/9 x (98.6 - 32)

C = 5/9 x (66.6)

C = 37 C

Check your answer to ensure it makes sense. At ordinary temperatures, a Celsius value is always lower than the corresponding Fahrenheit value. Also, it's helpful to keep in mind that the Celsius scale is based on the freezing and boiling points of water, where 0 C is the freezing point and 100 C is the boiling point. On the Fahrenheit scale, water freezes at 32 F and boils at 212 F.

Conversion Shortcut

You often don't need an exact conversion. If you're traveling to Europe, for example, and you know the temperature is 74 F, you might want to know the approximate temperature in Celsius. The website Lifehacker offers this tip on making an approximate conversion:

Fahrenheit to Celsius: Subtract 30 from the Fahrenheit temperature and then divide by two. So, using the approximation formula:

74 F – 30 = 44

44 / 2 = 22 C

(If you go through the previous formula's calculations for the exact temperature, you arrive at 23.3.)

Celsius to Fahrenheit: To reverse the approximation and convert from 22 C to Fahrenheit, multiply by two and add 30. So:

22 C x 2 = 44

44 + 30 = 74 C

Quick Conversion Table

You can save even more time by using predetermined conversions. The Old Farmer's Almanac offers this table for making quick conversions from Fahrenheit to Celsius.