Fahrenheit to Celsius Calculator

Fahrenheit and Celsius temperatures are two common scales, with the United States being by far the only region that predominantly uses Fahrenheit temperature to this day. So when comparing weather forecasts, recipes or thermometers from the US to other regions of the world a conversion is required. This calculator allows for instant conversion and also shows the temperature in Kelvin. By switching which scale you input into, you can convert both ways.

To convert Fahrenheit to Celsius, use this formula:

Subtract 32 from the temperature in degrees Fahrenheit and divide by 1.8 (or 9/5). Subtracting 32 corrects for the difference in the freezing points of the two scales, while dividing by 1.8 adjusts for the different size of a degree on each scale since there are fewer degrees between the boiling and freezing points of water on the Fahrenheit scale than on the Celsius scale.

For example, normal body temperature is 98.6°F. Subtracting 32 gives us 66.6, and dividing that result by 1.8 gives exactly 37°C. A summer heatwave of 86°F converts to (86 − 32) ÷ 1.8 = 30°C, while a pleasant room temperature of 68°F is 20°C.

To convert Celsius to Fahrenheit, do this:

To convert back, reverse the two steps. First multiply by 1.8 and then add 32.

Thus, 20 °C = 20 × 1.8 + 32 = 68 °F, and the boiling point of water, which is 100 °C, corresponds to 100 × 1.8 + 32 = 212 °F. To do this with a calculator, switch the input from Fahrenheit to Celsius and read the result in Fahrenheit.

Why -40° is the same in both temperature scales:

There is only one temperature at which the two scales read the same, -40 degrees Fahrenheit and -40 degrees Celsius. This is where the two lines cross. If you substitute °F = °C into the equation and solve for it, you get -40 as a result. So when someone says "negative forty," they don't have to specify which scale they are using.

A quick way to estimate in your head:

Since the exact formula is not suitable for mental calculations, here's a rough shortcut from Celsius to Fahrenheit. Double the temperature in Celsius and add 30. For 25 °C this gives 2 × 25 + 30 = 80 °F. The accurate value is 77 °F so it's within a few degrees of error, which is enough to decide whether or not to bring a jacket. To convert from Fahrenheit to Celsius, subtract 30 and then divide by two.

Useful temperatures to memorize:

The conversion is a little complicated so it's helpful to memorize some important temperatures.

• 0°C = 32°F - The temperature at which water freezes.

• 10°C = 50°F - a cold day.

• 20°C = 68°F - a pleasant room temperature.

• 30°C = 86°F - a hot summer day.

• 98.6 degrees Fahrenheit is normal body temperature.

• 100.4°F (38°C) is a commonly used general threshold for fever.

• 100°C = 212°F - The temperature at which water boils.

• −40 °C = −40 °F - this is the point at which the two temperature scales meet.

Fahrenheit to Celsius conversion table:

A handy reference. Any celsius value is calculated as (°F - 32) ÷ 1.8 and rounded to the specified number of decimal places.

Celsius to Fahrenheit conversion table:

The same relationship is reversed to convert Fahrenheit to Celsius. Any given Fahrenheit temperature can be converted to the Celsius equivalent with this equation: °F × 1.8 + 32 = °C.

What is the Fahrenheit temperature scale?

The Fahrenheit temperature scale was proposed in 1724 by the German physicist Daniel Gabriel Fahrenheit. He was one of the first to manufacture reliable mercury thermometers. In his temperature scale, water freezes at 32 °F and boils at 212 °F, so that the difference between these two temperatures is exactly 180 degrees.

The Fahrenheit temperature scale was the standard in English-speaking countries until the mid-20th century. Today it has been supplanted as an official or everyday temperature scale in most of the world except for the United States and some associated territories, so travelers, cooks, and students often need to convert from Fahrenheit to Celsius.

What is the Celsius temperature scale?

The Celsius temperature scale, formerly called the centigrade scale, was proposed by the Swedish astronomer Anders Celsius in 1742. It defines water's freezing point as 0 and its boiling point as 100, cleanly dividing that range into 100 degrees, which makes it very compatible with the metric system.

The Celsius temperature scale is the standard temperature scale used by nearly all countries and throughout the scientific community. It has a formal correspondence to the Kelvin temperature scale, with one degree of change in Celsius temperature corresponding to one degree of change in Kelvin temperature. Additionally, 0 °C is defined as being equal to 273.15 K.

Kelvin, Rankine, Réaumur - further temperature indications

In addition to the two common temperature scales this calculator can display three other temperature scales. Kelvin is an international system of units temperature scale used in science. It starts at absolute zero (0 K = −273.15 °C) and uses the same unit size as Celsius, so all that needs to be done is add 273.15.

If you open "Other Temperature Scales", the Rankine temperature scale and the Réaumur temperature scale will be shown. The relationship between the Rankine temperature scale and Fahrenheit temperature scale is similar to that of Kelvin temperature scale and Celsius temperature scale. It uses an absolute temperature scale with the same unit as degrees Fahrenheit, where 0 °R is absolute zero and water freezes at 491.67 °R. The Réaumur temperature scale is a historical temperature scale which was once widely used in Europe, setting the freezing point of water to be 0 degrees and boiling point to be 80 degrees.

The temperature unit conversion is only a general reference. Normal body temperature and fever values can vary from person to person, time of day, and method of measurement. Note that health information is for general guidance purposes only and does not constitute medical advice.