You can convert Fahrenheit to Celsius or vice versa by using simple addition, subtraction, multiplication or division operations. The next time you're given a temperature on the wrong scale, you'll be able to convert it in seconds!
Step
Method 1 of 6: Fahrenheit to Celsius
Step 1. Understand the scale for this temperature
The Fahrenheit and Celsius scales start at different numbers; 0° is the freezing point in Celsius, while for Fahrenheit the temperature is equivalent to 32°. In addition to starting at different temperatures, the two scales also increase at different rates. For example, the range from freezing to boiling point in degrees Celsius is 0-100°, while in degrees Fahrenheit the range is 32-212°.
Step 2. Reduce the Fahrenheit temperature by 32
Since the freezing point for Fahrenheit is 32 and the freezing point for Celsius is 0, start the conversion by subtracting the Fahrenheit temperature by 32.
For example, if Fahrenheit's initial temperature was 74 °F, subtract 74 by 32. 74-32 = 42
Step 3. Divide the result by 1, 8
The range from freezing to boiling point in Celsius is 0-100, while for Fahrenheit it is 32-212. That is, every 180 °F range equals 100 °C range. Express this ratio as 180/100, which if simplified will be 1.8, so to complete the conversion, divide the result by 1.8.
- For the example from step one, divide the result by 1.8, so that 42/1, 8 = 23 °C. Therefore, 74 °F = 23 °C.
- Note that 1.8 is equivalent to 9/5. If a calculator is not available or you prefer a fractional number, divide the result in the first step by 9/5 instead of 1, 8.
Method 2 of 6: Celsius to Fahrenheit
Step 1. Understand the scale for this temperature
The same rules for difference in scale apply when converting Celsius to Fahrenheit, so you're still using the 32 difference and the 1.8 scale difference, but in reverse order.
Step 2. Multiply the Celsius temperature by 1, 8
To convert the temperature from degrees Celsius to Fahrenheit, reverse the process. Start by multiplying the Celsius temperature by 1.8.
For example, if you have a temperature of 30 °C, first multiply by 1.8 or 9/5, so that 30 x 1.8 = 54
Step 3. Add the result by 32
You've corrected the difference in the temperature scale, and now you have to correct the difference in the starting point the same as in step one. To do this, add 32 to Celsius x 1.8, with the final result in Fahrenheit.
Add 32 by 54, which is the result of step 3. 54+32 = 86 °F. Therefore, 30 °C is equivalent to 86 °F
Method 3 of 6: Celsius to Kelvin
Step 1. Understand the scale for this temperature
Scientists understand that the Celsius scale is derived from the Kelvin scale. Although the gap between Celsius and Kelvin is much larger than the gap between Celsius and Fahrenheit, one similarity between Celsius and Kelvin is that they both increase at the same rate. The ratio for Celsius to Fahrenheit is 1:1, 8, the ratio for Celsius to Kelvin is 1:1.
If the freezing point number for a high Kelvin looks odd, which is 273, 15, it's because the Kelvin scale is based around absolute zero, which is 0 °K
Step 2. Add 273, 15 to the Celsius temperature
Although 0 °C is the freezing temperature of water, scientists do understand that 0 °C is 273.15 °K. Since both scales increase at the same rate, add 273, 15 to convert Celsius to Kelvin.
For example, if you have a temperature of 30 °C, simply add 273, 15, so 30+273, 15 = 303, 15 °K
Method 4 of 6: Kelvin to Celsius
Step 1. Understand the scale for this temperature
The 1:1 ratio for each degree Celsius and Kelvin is still valid when converting Kelvin to Celsius. You usually just remember the number 273, 15 and perform the opposite operation of converting Celsius to Kelvin.
Step 2. Reduce the Kelvin temperature by 273, 15
If you need to convert the temperature from Kelvin to Celsius, simply reverse the operation and subtract 273, 15. Let's say you have a Kelvin temperature of 280 °K. Subtract 280 by 273, 15 to get the Celsius temperature. 280-273, 15 = 6, 85 °C.
Method 5 of 6: Kelvin to Fahrenheit
Step 1. Understand the scale for this temperature
One of the most important things to remember when converting between Kelvin and Fahrenheit is the increment ratio. Since the ratio of Kelvin and Celsius is 1:1, the ratio also applies to Fahrenheit, meaning that every 1°K change equals 1.8°F.
Step 2. Multiply by 1, 8
To correct the 1K:1, 8F scale, the first step in converting Kelvin to Fahrenheit is to multiply by 1.8.
Say you have a temperature of 295°K. Multiply that number by 1.8, so that 295 x 1.8 = 531
Step 3. Subtract the result by 459, 7
Just as you must correct the starting point of the scale by adding 32 when converting Celsius to Fahrenheit, do the same when converting Kelvin to Fahrenheit. However, 0 °K = -459, 7 °F. Since the number to be added is actually a negative number, you will need to subtract the number.
Subtract 531 by 459, 7, so that 531-459, 7 = 71.3 °F. Therefore, 295°K = 71.3°F
Method 6 of 6: Fahrenheit to Kelvin
Step 1. Reduce the Fahrenheit temperature by 32
On the other hand, to convert Fahrenheit temperature to Kelvin temperature, the easiest way is to convert it to Celsius and then convert the result to Kelvin. That is, start by reducing it by 32.
Say you have a temperature of 82 °F. Subtract that number by 32, so 82-32 = 50
Step 2. Multiply the result by 5/9
When converting Fahrenheit to Celsius, the next step is to multiply by 9/5, or divide by 1.8 if a calculator is available.
50 x 5/9 = 27.7, which is the final Celsius temperature
Step 3. Add 273, 15 to this number
Since the difference between Celsius and Kelvin = 273, 15, the Kelvin temperature is obtained by adding 273, 15.
So: 273, 15+27, 7 = 300, 8. Therefore, 82 °F = 300, 8 °K
Tips
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Here are some key conversion numbers to keep in mind:
- Water freezes at 0 °C or 32 °F.
- Body temperature is usually 37 °C or 98.6 °F.
- Water boils at 100 °C or 212 °F.
- At -40, both temperatures are the same.
- Double-check the calculation you did, so you are absolutely sure of the final result of the calculation.
- When dealing with an international audience, don't use the words 'centigrade' or 'celsius' but instead 'degrees Celsius'.
- Remember that Kelvin is always 273.15° greater than Celsius.
- You can also use the formula C = 5/9 (F-32) to convert Fahrenheit to Celsius, and 9/5C = F-32 to convert Celsius to Fahrenheit. This formula is a shortened version of this equation: C/100 = (F-32)/180. Since the freezing point is in the 212 range on the Fahrenheit thermometer, you should reduce the temperature in Fahrenheit by 32 F (F-32). Then you also have to subtract it from 212, that's the secret of the number 180. This is done, the two intervals are the same and we will get the "long version" of the equation.
