This is for my dear friends who will soon be travelling to Spain:

When I was in elementary school, we were taught, drilled and tested on the formulas for converting temperature measurements between Fahrenheit and Celsius. Celsius was known as Centigrade back then, but they both begin with C so it doesn't matter. :)

F = 9/5 x C + 32

C = 5/9 x (F - 32)

It was an all but useless exercise. How often do most people need to do those conversions? In the science lab, we use Celsius; otherwise, Fahrenheit. Except at our house, when I was young. The thermometer that my father bought and installed outside our window read only in Celsius, so I was kept busy converting it into the more familiar numbers. Even so, I never really learned the conversion formulas; I never could remember which way they went. How liberating it was, many years later, when I realized that I could easily figure that out, knowing 0C = 32F (water freezes) and 100C = 212F (water boils).

It wasn't until I was more than 30 years outside of elementary school, vacationing in New Zealand, that I discovered even greater freedom. All temperatures there are in Celsius (as they are in most of the world), and those old formulas were just too clumsy. So I amused myself by developing a much handier formula that was just fine for my purposes.

When you are visiting the Celsius world, and you hear that the outside temperature is 25 degrees, and you're wondering if you should wear short sleeves or a heavy jacket, just multiply that temperature by 2 and add 30. Easy to do in your head, and it quickly tells you that the temperature is about 25 x 2 + 30 = 80 degrees. Definitely short sleeves.

F = 2 x C + 30

It's easy to remember, easy to work out in your head, and accurate to within a few degrees over the range a tourist is interested in. (Just don't plan to visit Antarctica.) If you want to be more accurate, just remember that the result of this formula is exact at 50 degrees Fahrenheit, a little too high for higher temperatures, and a little too low for lower ones.

For Celsius users visiting the United States (is there anywhere else that uses Fahrenheit?), the formula **C = 1/2 x (F - 30)** is almost as easy to use.

You're welcome; I'm glad you like it.

Really helpful. Thank you

This is great, easy to remember/figure out...

try to convert using this formula

32 F to C

should be o C, but it comes 1 C

Correct: the quick conversion is almost always wrong, but - and that's what matters - almost always close.

Really, the number of people who read this post but don't understand it at all is rather scary. What are schools teaching if so many people fail at such basic reading comprehension!

Why don't we just start using metric system - and Celsius - as any other good boy on this planet?? Easier and more effective...

Will this work for my tests in math

Not unless you're asked for an estimate, Christa. Most math teachers want the exact answer.

Thanks! Leaving for Australia next week and this is a hot tip! Gracias, gracias!

Another couple of good ones to remember are 61F = 16C and 82F = 28C.

Together with 50 = 10, you should be able to make an educated guess when trying to decide what the temperature is..

Enjoy!

Thanks, Wendy. They're not exact, but absolutely close enough for these purposes—and easy to remember.

Great. The wife is always bugging me but now I can do it in my head. Much thanks for this simple formula.

**Excerpt:**A comment made by Janet to my Quick Tourist's Conversion between Fahrenheit and Celsius post inspired these thoughts, and it seemed better to give them their own post rather than to comment on that one.: The Orlando Sentinel of January 31 contained an...

**Weblog:**Lift Up Your Hearts!

**Date:**February 8, 2013, 6:31 am