An easy way to convert degrees Fahrenheit to Celsius

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

15 February 2009

Cookery is not an exact science. It’s like medicine; one doctor will prescribe one teaspoon of some drug while another equally qualified physician will order you to take one tablespoon of the same concoction for the same ailment. Still, when you start measuring temperatures, cooking suddenly changes its character and becomes an exact science.

The problem arises because there are two commonly used scales – the Celsius and the Fahrenheit. When preparing a meal, especially when baking, the cook has to be careful to ensure that he sets the correct value and in the correct scale.

200 degrees Fahrenheit, for example is very different from 200 degrees celsius. One is much hotter than the other. Thus the question arises: Is there a quick method of converting temperatures from one scale to the other?

To find out, we need to understand the basis of the two scales. The Celsius scale is named after its developer, Anders Celsius. In this scale, the freezing point of pure water is designated zero and the boiling point 100 degrees; both temperatures being measured at sea level.

The Fahrenheit scale is also named after its developer, Gabriel Fahrenheit, and its zero is the freezing point of a solution of ammonia chloride in water. The second reference point was supposed to be the human body temperature, designated 100 degrees. Due to some practical difficulties, however, Fahrenheit decided to change it from 100 to 98 degrees.

Now, when this scale is interpolated and extrapolated, it turns out that the freezing point of water is 32 degrees F and the boiling point is 212 degrees F. The number of degrees between these two points is 180, compared to 100 on the Celsius scale.

Thus one degree range in Fahrenheit is equal to 1.8 degrees in celsius. Therefore, we might expect that to convert from Celsius to Fahrenheit, we simply multiply by 1.8 (or by 2, if we don’t have a calculator at hand).

Let’s try with an example: What Fahrenheit temperature is equivalent to 100 degrees celsius? Multiplying 100 by 1.8 gives 180 degrees. This is wrong because we know 100 degrees celsius is the boiling point of water, but in the Fahrenheit scale, it is 212 degrees. We have missed the answer by 32 degrees.

Now that is inspiring: after multiplying by two, shouldn’t we add 32 to the result? Let’s see with another example: What Fahrenheit temperature is equivalent to zero Celsius?

Zero multiplied by 1.8 is zero! Adding 32 to this value yields 32 degrees. Thus we can conclude that to get Fahrenheit from Celsius, we multiply by 1.8 (or 2 when baking and there is no calculator in the kitchen!) and then ad 32.

The reverse is equally easy: to get Celsius from Fahrenheit, we start by subtracting 32 and then divide by 1.8 (or 2 when in a hurry).