There are three major temperature scales: Celsius, Kelvin, and Fahrenheit. It’s easy to convert between them. All you need is a few simple tricks.

Celsius and Kelvin degrees measure exactly the same temperature difference. The scales are different only because the Celsius scale uses the freezing point of water as 0 degrees, while Kelvin uses absolute zero instead. In Celsius, absolute zero is -273.15 degrees.

That means that all you have to do to convert Kelvin to Celsius is to subtract 273.15 from the temperature, or just 273 if you’re rounding off. If you’re converting Celsius to Kelvin, you have to add 273 degrees.

* Celsius plus 273 equals Kelvin. *

* Kelvin minus 273 equals Celsius. *

Celsius and Fahrenheit degrees do not measure the same temperature difference. In Celsius, it’s exactly 100 degrees between water’s freezing point (0 degrees) and boiling point (100 degrees). In Fahrenheit, the difference is 180 degrees between water’s freezing point (32 degrees) and boiling point (212 degrees). This means that a temperature difference of 100 degrees in Celsius is the same as a temperature difference of 180 degrees in Fahrenheit. Each Celsius degree is equal to 1.8 degrees Fahrenheit.

It’s a little more complicated than before, but all you have to do to convert Fahrenheit to Celsius is to subtract 32, then divide by 1.8. If you’re converting Celsius to Fahrenheit, you have to add 32 first, then multiply by 1.8. It’s even easier if you do it as a fraction, because 1.8 equals 9/5. The reason you have to add or subtract 32 first is because in Fahrenheit, the freezing point of water is 32 degrees above 0.

* (Fahrenheit minus 32) times 5/9 equals Celsius. *

* (Celsius plus 32) times 9/5 equals Fahrenheit. *

But for most temperatures, there’s a much faster way to do it. Every 10 degree difference in Celsius is an 18 degree difference in Fahrenheit. The freezing point of water is 0 Celsius, or 32 Fahrenheit. For every 10 degrees change in Celsius, the Fahrenheit temperature changes by 18 degrees.

* 0 Celsius equals 32 Fahrenheit *

* 10 Celsius equals 50 Fahrenheit *

* 20 Celsius equals 68 Fahrenheit *

* 30 Celsius equals 86 Fahrenheit *

* 40 Celsius equals 104 Fahrenheit *

You can keep adding or subtracting 10s/18s indefinitely. If you want more precision, add or subtract 5s/9s instead. It’s exactly the same thing as multiplying or dividing by the fraction 5/9.

Notice that if you take it down instead of up within the range of normal weather temperatures, Celsius and Fahrenheit temperatures get closer and closer together. At -40 degrees, the Fahrenheit and Celsius temperatures are exactly the same!