Fahrenheit to Celsius, fast

If you’re wanting to convert Fahrenheit to Celsius, the real formula looks like this:

(°F — 32) / 1.8 = °C

Or going from Celsius to Fahrenheit:

(°C * 1.8) + 32 = °F

That’s accurate, but hard to do in your head. Here are two quick ways to do it instead; just memorize a few numbers (from whichever method you prefer) and you’re all set.

30 and half

This is the method I generally use. It takes the formula from above, but simplifies it a lot. It’s not precise, but good enough for normal use.

If you have a number in Fahrenheit, just subtract 30 and then divide it in half. For example if it’s 70° Fahrenheit right now, subtract 30 (so you have 40) and divide by 2 = 20°. The real number is 21.1, so you’re certainly close enough.

To go the other way, double it and then add 30. If someone said it was a cool 10° Celsius right now, just double it (so you have 20) and then add 30 = 50°. In this case, that 50° is exactly accurate.

Remember four numbers

A new way I saw to do this is to just remember four numbers: 04 16 28 40

In most any case, just take any of those as Celsius and reverse the numbers for Fahrenheit.