How to Convert Between Fahrenheit, Celsius, and Kelvin

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You can convert degrees Fahrenheit to degrees Celsius or vice versa by using simple addition, subtraction, multiplication, and division. Next time you’re given the temperature in the wrong scale, you’ll be able to convert it in just a matter of seconds!

Method 1
Method 1 of 6:

Converting Fahrenheit to Celsius

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  1. The Fahrenheit and Celsius scales begin at a different number—where 0° Celsius is freezing, that equivalent temperature in Fahrenheit is 32°. In addition to starting at a different temperature, the two scales rise at different rates as well. For instance, the range from freezing to boiling in degrees Celsius is 0-100°, and the same range in degrees Fahrenheit is 32-212°. [1]
  2. Since freezing for Fahrenheit is 32 and freezing for Celsius is 0, you begin the conversion by subtracting 32 from the Fahrenheit temperature. [2]
    • For example, if your initial Fahrenheit temperature is 74°F, just subtract 32 from 74. 74-32 = 42. [3]
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  3. Divide the result by 1.8. The range for freezing to boiling in Celsius is 0-100 whereas it's 32-212 in Fahrenheit. This is the same as saying that for every 180° Fahrenheit range, there is only a 100° Celsius range. You can express that as 180/100, which when simplified equals 1.8, so to finish the conversion you must divide by 1.8.
    • For the example from step one, divide your result, 42, by 1.8. 42/1.8 = 23°C. Therefore, 74°F can be converted to 23°C.
    • Note that 1.8 is the equivalent of 9/5. If you don't have a calculator or prefer working with fractions, you can divide your result from the first step by 9/5 instead of 1.8.
  4. Here are a few conversions so you can see whether your result makes sense. If you get a result that doesn't fit this scale, check your math again. You may have forgot to subtract before dividing.



    ºFahrenheit ºCelsius (approx)
    -40

    -40
    0

    -18
    32

    0
    60

    16
    100

    38
    150

    66
    212

    100
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Method 2
Method 2 of 6:

Converting Celsius to Fahrenheit

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  1. Since the same rules in the scale differences apply when converting Celsius to Fahrenheit as the opposite, you'll still be using the difference of 32 and the scale difference of 1.8. You just use them in the reverse order.
  2. Multiply the Celsius temperature by 1.8. If instead, you want to convert the temperature from degrees Celsius to degrees Fahrenheit, you can simply reverse the process. Begin by multiplying the Celsius temperature by 1.8. [4]
  3. 3
    Work with a 30°C temperature. For example, if you're working with the temperature 30°C, you should first multiply it by 1.8, or 9/5. 30 x 1.8 = 54. [5]
  4. Add 32 to the result. Now that you have corrected for the differences in scale, you still must correct for the difference in starting points as in step one. To do this, add 32 to the Celsius x 1.8 temperature, and you will have the final temperature in degrees Fahrenheit.
    • Add 32 to 54, which was the result from step 3. 54 + 32 = 86°F. Therefore, 30°C is equivalent to 86°F.
  5. 5
    Check your answer. If your answer doesn't fit between two lines of this chart, you've probably made a math error. Remember to multiply by 1.8 before adding 32.

    ºCelsius ºFahrenheit
    -40

    -40
    0

    32
    15

    59
    30

    86
    60

    140
    100

    212
    200

    392
  6. 6
    Make a general comparison. A more general way to compare the two is to realize that every 5°C equals 9°F:

    ºCelsius ºFahrenheit ºCelsius ºFahrenheit
    -50

    -58

    0

    32
    -45

    -49

    5

    41
    -40

    -40

    10

    50
    -35

    -31

    15

    59
    -30

    -22

    20

    68
    -25

    -13

    25

    77
    -20

    -4

    30

    86
    -15

    5

    35

    95
    -10

    14

    40

    104
    -5

    23

    45

    113

    50

    122
  7. 7
    Understand the conversion. Given the 1.8 conversion factor, each 1°C difference equals 1.8°F, with that idea highlighted in the 10-15°C range:

    ºCelsius ºFahrenheit ºCelsius ºFahrenheit
    -1

    30.2

    10

    50.0
    0

    32.0

    11

    51.8
    1

    33.8

    12

    53.6
    2

    35.6

    13

    55.4
    3

    37.4

    14

    57.2
    4

    39.2

    15

    59.0
    5

    41.0

    16

    60.8
    6

    42.8

    17

    62.6
    7

    44.6

    18

    64.4
    8

    46.4

    19

    66.2
    9

    48.2

    20

    68.0
  8. If one rounds the Fahrenheit values, the difference in Fahrenheit from the nearest 5 or 10°C has the pattern 2,4,5,7:

    ºCelsius ºFahrenheit (rounded)
    5

    41 = 41+0 = 41-0
    6

    43 = 41+2 = 50-7
    7

    45 = 41+4 = 50-5
    8

    46 = 41+5 = 50-4
    9

    48 = 41+7 = 50-2
    10

    50 = 50+0 = 50-0
    11

    52 = 50+2 = 59-7
    12

    54 = 50+4 = 59-5
    13

    55 = 50+5 = 59-4
    14

    57 = 50+7 = 59-2
    15

    59 = 59+0 = 59-0
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Method 3
Method 3 of 6:

Converting Celsius to Kelvin

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  1. Scientists understand the Celsius scale as derived from the Kelvin scale. [6] Though the gaps between Celsius and Kelvin are even larger than the gaps between Celsius and Fahrenheit, one thing that Celsius and Kelvin have in common is that they rise at the same rate. Whereas the ratio for Celsius to Fahrenheit is 1:1.8, the ratio for Celsius to Kelvin is 1:1. [7]
    • If it seems odd that freezing for Kelvin would be such a high number — 273.15 — it's because the Kelvin scale is based around absolute zero, which is 0K.
  2. Though 0°C is the freezing temperature of water, scientists actually understand 0°C as 273.15K. [8] Since the two scales rise at the same rate, then converting Celsius to Kelvin always means simply adding 273.15.
    • For example, if you're working with the temperature 30°C, just add 273.15 to that. 30 + 273.15 = 303.15K.
  3. Here's a rough scale so you can test whether your answer makes sense. Note that the Celsius and Kelvin scales increase at the same rate, so the two numbers are always exactly 273.15 apart.
    • If you start with an integer value of degrees Celsius, your result in kelvins will end in the decimal .15.
    • The lowest possible temperature is -273.15ºC = 0 kelvins. If your result involves negative kelvins, you either made a math mistake or the problem uses impossible values.

      ºCelsius kelvins
      -100

      173.15
      -50

      223.15
      0

      273.15
      50

      323.15
      100

      373.15
      200

      473.15
      500

      773.15
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Method 4
Method 4 of 6:

Converting Kelvin to Celsius

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  1. The 1:1 ratio for each degree Celsius and Kelvin still applies while converting Kelvin to Celsius. You mostly need to remember the 273.15 number and perform the opposite operation as when you convert Celsius to Kelvin.
  2. If instead you need to convert the temperature from Kelvin to Celsius, you can simply reverse the operation and subtract 273.15. Let’s say you're starting with a Kelvin temperature of 280K. Just subtract 273.15 from 280 to get the Celsius temperature. 280K - 273.15 = 6.85°C.
  3. If the two values you have don't fit the pattern described in this table, check for math mistakes.
    • If you start with an integer value of kelvins, your result in degrees Celsius will end in the decimal .15 (if Celsius is negative) or .85 (if Celsius is positive).
    • Note how the difference between kelvins and Celsius becomes less important for very large numbers. Once you're dealing with 6+ digits, the difference is often within your margin of error.

      kelvins ºCelsius
      0

      -273.15
      5

      -268.15
      50

      -223.15
      200

      -73.15
      500

      226.85
      1,000

      726.85
      100,000

      approx. 99,700
      10 million

      very close to 10 million
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Method 5
Method 5 of 6:

Converting Kelvin to Fahrenheit

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  1. One of the most important things to remember while converting between Kelvin and Fahrenheit is the rise ratio. Since Kelvin has a 1:1 ratio with Celsius, it has the same ratio to Fahrenheit as Celsius, which is to say that for every 1K, Fahrenheit changes by 1.8°F. [9]
  2. In order to correct for the 1K:1.8F scale, the first step in converting Kelvin to Fahrenheit is multiplying by 1.8.
    • Let’s say you're starting with a temperature of 295K. Just multiply that number by 1.8. 295 x 1.8 = 531.
  3. Just as we must correct for the starting point of the scale by adding 32 when converting Celsius to Fahrenheit, we must also do the same when converting Kelvin to Fahrenheit. However, 0K = -459.7°F. [10] Since the number we have to add is actually a negative number, that means we must simply subtract the number.
    • Just subtract 459.7 from 531. 531 - 459.7 = 71.3 °F. Therefore, 295K = 71.3 °F.
  4. If your conversion doesn't fit between two lines of this table, try again. You may have made a math mistake, or forgotten to multiply before subtracting.
    • If you start with an integer value of kelvins, your answer in degrees Fahrenheit will end in the decimal .67 (if ºF is negative) or .33 (if ºF is positive).

      kelvins ºFahrenheit
      0

      -459.67
      5

      -450.67
      50

      -369.67
      200

      -99.67
      500

      440.33
      1,000

      1,340.33
      100,000

      approx 180,000.
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Method 6
Method 6 of 6:

Converting Fahrenheit to Kelvin

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  1. On the other hand, to convert a Fahrenheit temperature to a Kelvin temperature, it’s easiest to convert to Celsius and then make the conversion to Kelvin from there. This means we begin by subtracting 32.
    • Let’s say the temperature is 82°F. Subtract 32 from that number. 82 - 32 = 50.
  2. When converting Fahrenheit to Celsius, the next step is to multiply by 5/9–or divide by 1.8 if you have a calculator around.
    • 50 x 5/9 = 27.7, which is the Fahrenheit temperature now converted to Celsius.
  3. Since the difference between Celsius and Kelvin = 273.15, you can then get the Kelvin temperature by adding 273.15.
    • 273.15 + 27.7 = 300.8. Therefore, 82°F = 300.8K.
  4. Compare your result to this table to see if it makes sense. If it doesn't seem to fit the scale, try again. Make sure you subtract before multiplying.
    ºFahrenheit kelvins (approx)
    -25

    241
    0

    255
    32

    273.15 exactly
    70

    294
    100

    311
    150

    339
    212

    373.15 exactly
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      Tips

      • Double check your math, it will make you more confident in your final answer.
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      • Remember that Kelvin is always 273.15° more than Celsius.
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      • 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. These formulas are short versions of this equation: C/100=(F-32)/180 . As freezing point is within the range of 212 in the F thermometer, we have to subtract it, 32ºF, from F temperatures ( F-32 ) and we also have to subtract it from 212, and that's how we get the 180 cipher. This been done, both intervals are equal and we get the "long version" equation.
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      References

      1. ↑ http://www.mathsisfun.com/temperature-conversion.html
      2. ↑ http://www.mathsisfun.com/temperature-conversion.html
      3. ↑ http://www.mathsisfun.com/temperature-conversion.html
      4. ↑ http://www.mathsisfun.com/temperature-conversion.html
      5. ↑ http://www.mathsisfun.com/temperature-conversion.html
      6. ↑ http://www.metric-conversions.org/temperature/fahrenheit-to-celsius.htm
      7. ↑ http://www.metric-conversions.org/temperature/fahrenheit-to-celsius.htm
      8. ↑ http://www.metric-conversions.org/temperature/fahrenheit-to-celsius.htm
      9. ↑ http://www.metric-conversions.org/temperature/fahrenheit-to-celsius.htm
      1. ↑ http://www.rapidtables.com/convert/temperature/how-kelvin-to-fahrenheit.htm

      About This Article

      Article Summary X

      To convert Fahrenheit to Celsius, subtract 32 from the Fahrenheit temperature and then divide your answer by 1.8. To convert from Celsius to Fahrenheit, multiply the Celsius temperature by 1.8 and then add 32 to your answer. If you're trying to convert Celsius to Kelvin, just add 273.15 to the Celsius temperature. To learn how to convert Fahrenheit to Kelvin, scroll down!

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