How to convert temperature from Celcius to Fahrenheit

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

29 November 2020

After reading last week’s article on human body temperature measurements, Mary Musyoka finally got a chance to ask a question that has bothered has since primary school: what is the conversion factor to change from degrees Fahrenheit to degrees Celcius?

She says: “I see some recipes with temperatures in Fahrenheit yet my cooker is labelled in Celcius. It is annoying to keep asking google to convert, so, if I knew the factor, I could just do it in my head. The same way we know that one inch is 2.5cm.”

Unfortunately, it is not that easy for temperature; there is no conversion factor for converting from Fahrenheit to Celcius. The reason is that the two scales do not start at the same point – zero degrees-F is not zero degrees-C.

The Celsius scale is based on the behaviour of pure water. Zero is the temperature at which it freezes/melts and 100 is the boiling/condensation point (measure at sea-level).

It is important to specify the altitude because the amount of atmospheric pressure affects the behaviour of matter. The boiling temperature of water in Nairobi, for example, is about 94 degrees-C while in Mombasa it is 100 degrees-C.

It is not clear what the zero of the Fahrenheit scale is. One story says it was the freezing point of a mixture sea water and ammonium chloride. Another one claims it was the lowest temperature recorded in the city of Gdańsk, Poland, during the winter of 1708/09.

Whatever the true position, what we know today is that zero degrees-C corresponds to 32 degrees-F and 100-C to 212-F, respectively. The span between melting and boiling of water in the Celcius scale is 100 units while in Fahrenheit it is 180.

So, each degree in Celcius is equal to 1.8 in Fahrenheit. However, we cannot simply divide the Fahrenheit amount by 1.8 to convert to Celcius. After all; dividing 32 by 1.8 gives 17.8 degrees-C. This is not correct! 32-F is equal to 0-C.

Therefore, we must first subtract 32 from the Fahrenheit temperature. Doing that brings the two scale to the same starting point. Thus 32 – 32 = 0; and 0 divided by 1.8 is 0.

We may test by applying the same steps to the boiling point, thus: 212 – 32 = 180; and 180 divided by 1.8 is 100. Thus 212 degrees-F is equal to 100 degrees-C.

So, for any other temperature, start by subtracting 32 from the Fahrenheit figure, then divide the result by 1.8. QED.