When one goes to a physician visit the first thing the nurse shall do to put thermometer under the tongue. That is to take the body temperature. A reading of 97-98 degree is considered normal. Now the question arises about the unit/scale of the temperature reading. Various scales/units are used to represent temperature measurements. The instrument like thermometer used to measure the temperature is calibrated to represent a particular unit.

Though a temperature measurement is represented in different units it represents the same thing. That is why a unit conversion is needed to convert from one unit to other unit. The temperature can be represented in four units Fahrenheit (⁰F), Celsius (⁰C), Kelvin (⁰K), or Rankine (⁰R). Body temperature of 97-98 degree mentioned above is actually in ⁰F. The Celsius is calibrated so that 0 ⁰C means the freezing point of water when liquid water changes to ice) and 100 ⁰C means the boiling point of water when liquid water changes to steam. The freezing point of water in Fahrenheit is 32 ⁰F, in Kelvin is 273.15 ⁰K and in Rankine is 459.67 ⁰R. By definition 0 ⁰K, 0 ⁰R, -273.15 ⁰C, -523.67 ^0F are called absolute zero temperature. In USA Kelvin is used as absolute temperature. The Rankine is not used in USA.

There are equations for converting Fahrenheit scale to other scales. The same equations can also be used to convert other temperature scales to Fahrenheit scale. The following equations are used for conversion:

C/5  =  (F – 32)/9…………..(1)

C = K – 273.15 …………    (2).

C = (R – 491.67)(5/9) ……  (3)  

From equation (1) we can get the other equation for converting Fahrenheit to Celsius

            C  =  (5/9) (F – 32)                                    (4)

            K = C + 273.15 = (5/9) (F-32) + 273.15   (5)

            R = (C + 491.67)(9/5) = F + 459.67         (6)

So,

Equation (4) converts Fahrenheit to Celsius

Equation (5) converts Fahrenheit to Kelvin

Equation (6) converts Fahrenheit to Rankine

One can code the above equations in a calculator so that an input value of ⁰F shall give equivalent output in ⁰C, ⁰K, and ⁰R, There are many web pages that also provide buttons for input value in ⁰F and generates outputs in ⁰C, ⁰K, and ⁰R.

Below is provided a chart to compare temperature values in different scales:

Celsius          -50                                    0                                                                    100

Fahrenheit     -58                                   32                                                                   212

Kelvin K      223.15                               273.15                                                           373.15

Rankine        401.67                              491.67                                                           671.67