Introduction to temperature - including Celsius, Fahrenheit, Kelvin and Rankine definitions - an online temperature converter

Temperature (sometimes called thermodynamic temperature) is a measure of the average kinetic energy of a systems particles. Temperature is the degree of "hotness" ( or "coldness"), a measure of the heat intensity.

When two objects of different temperatures are in contact, the warmer object becomes colder while the colder object becomes warmer. It means that heat flows from the warmer object to the colder one.

Temperature Converter

Convert between oC (Celsius), oF (Fahrenheit), K (Kelvin) and oR (Rankine) with the calculator below:


oC oF K oR

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Degree Celsius (oC) and Degree Fahrenheit (oF)

A thermometer can help us determine how cold or how hot a substance is. Temperatures in science (and in most of the world) are measured and reported in degrees Celsius (oC). In the U.S., it is common to report temperature in degrees Fahrenheit (oF). On both the Celsius and Fahrenheit scales the temperature at which ice melts (water freezes) and the temperature at which water boils, are used as reference points.

  • On the Celsius scale, the freezing point of water is defined as 0 oC, and the boiling point of water is defined as 100 oC.
  • On the Fahrenheit scale, the water freezes at 32 oF and the water boils at 212 oF.

On the Celsius scale there are 100 degrees between freezing point and boiling point of water, compared to 180 degrees on the Fahrenheit scale. This means that 1 oC = 1.8 oF (check the section about temperature difference below).

Thus the following formulas can be used to convert temperature between the two scales:

tF = 1.8 tC + 32

   = 9/5 tC + 32         (1)

tC = 0.56 (tF - 32)

    = 5/9 (tF - 32)         (2)


tC = temperature (oC)

tF = temperature (oF)

temperature celcius fahrenheit diagram

Comparing Celsius and Fahrenheit:

oC oF
-20 -4
-15 5
-10 14
-5 23
0 32
5 41
10 50
15 59
20 68
25 77
30 86
35 95
40 104
45 113
50 122

Example - A patient with SARS (Severe Acute Respiratory Syndrome) has a temperature of 106 oF. What is the temperature in Celsius?

tC = 5/9 ((106 oF) - 32)

    = 41.1 oC

Temperature Conversion Table - oC vs oF

temperature conversion table chart

Temperature Difference - degree Celsius versus degree Fahrenheit

Note that for temperature difference - as used in heat loss diagrams

  • 1 degree Celsius of temperature difference equals 1.8 degree Fahrenheit of temperature difference

dtC = 0.56 dtF     (3)

dtF1.8 dtC    (3b)


dtF = temperature difference (oF)

dtC = temperature difference (oC)

Example - Temperature Difference between 100 oC to 50 oC

Temperature difference in degrees Celsius:

dtC = (100oC) - (50oC)

              = 50 (oC)

Temperature difference in degrees Fahrenheit calculated by using (1)

tF(100oC) = 1.8 (100 oC) + 32

              = 212 oF

tF(50oC) = 1.8 (50 oC) + 32

            = 122 oF

dtF = tF(100oC) - tF(50oC)

      = 90 (oF)

Temperature difference in degrees Fahrenheit calculated by using (3)

dtF = 1.8 (50 oC)

     = 90 oF

Kelvin - K

Another scale (common in science) is Kelvin, or the Absolute Temperature Scale. On the Kelvin scale the coldest temperature possible, -273 oC, has a value of 0 Kelvin (0 K) and is called the absolute zero. Units on the Kelvin scale are called Kelvins (K) and no degree symbol is used.
Because there are no lower temperatures than 0 K  - the Kelvin scale does not have negative numbers.

The Kelvin has the same incremental scale as the Celsius scale and one unit Kelvin is equal in size to one unit Celsius:

1 unit Kelvin  = 1 unit oC

To calculate a Kelvin temperature, add 273 to the Celsius temperature:

tK = tC + 273.16         (3)

Example - What is the normal body temperature of 37 oC in the Kelvin scale?

tK = tC + 273.16 = (37 oC) + 273.16

    = 310.16 K

Degree Rankine - R

In the English system the absolute temperature is in degrees Rankine (R), not in Fahrenheit:

tR = tF + 459.67         (4)

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