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.
The Fahrenheit (symbol: °F) is a unit of temperature that was widely used prior to metrication. It is currently defined by two fixed points: the temperature at which water freezes, 32°F, and the boiling point of water, 212°F, both at sea level and standard atmospheric pressure. The interval between the freezing and boiling point is divided into 180 equal parts.
The Celsius (symbol: °C) is an SI (International System of Units) derived unit of temperature. It is defined based on the SI unit of temperature, the kelvin. The Celsius and Kelvin scales are precisely related, with a one-degree change in Celsius being equal to a one degree-change in kelvin. The kelvin (and thus Celsius) is defined based on the Boltzmann constant, k, which equals 1.380649 × 10-23 when expressed in the unit J·K-1, a unit equivalent to kg·m2·s-2·K-1. The kilogram, meter, and second, are defined based on Planck's constant, h, the speed of light, c, and cesium frequency, ΔνCs.
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.
1) Subtract 32 from the Fahrenheit temperature.
2) Multiply this number by five.
3) 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:
1) 80 F – 32 = 48
2) 5 x 48 = 240
3) 240 / 9 = 26.7 C
Celsius to Fahrenheit ►