## Temperature Measurement vs Temperature Difference

Do not confuse a temperature measurement (for example, T = 25 °C, read as ‘twenty-five degrees Celsius’) with a temperature difference (ΔT=25 C°, read as ‘twenty-five Celsius degrees’).

You can convert a temperature in °C to Fahrenheit (°F), Rankine (°R), and kelvins. But you cannot ‘convert’ a temperature difference in the same manner. For example, a ΔT of 25 C° requires the same change in energy as a ΔT of 25 kelvin degrees. And, believe it or not, a ΔT of 45 F° requires the same change in energy as a ΔT of 45 R° (and no, I didn’t mean to write 25 F°).

The ‘conversion’ is the scale factor 1.8 (which is 9/5). So, an increase in temperature of 25 Celsius degrees represents the same energy increase as an increase in temperature of 45 Fahrenheit degrees, because 45=(25)(1.8). This just stems from the fact that a Celsius degree represents 1.8 times as much energy change as a Fahrenheit degree (just as a foot represents a length measurement 12 times as long as an inch).

As an illustration, the ΔT from ice water to boiling water at normal atmospheric pressure is 100 C°. In Fahrenheit it’s a ΔT of 180 F° (because 212-32=180). But the energy increase is the same! Therefore, ΔT(100 C°) = ΔT(180 F°).