Wednesday, May 23, 2018

C is for Conversions -- EASY method to convert between Fahrenheit and Celcius

Either using Celcius or Fahrenheit, ice fishing is a COLD pastime! :) 

Temperature conversions!  How comfortable are you with converting from Fahrenheit to Celcius or from Celcius to Fahrenheit?  Well, truthfully, nowadays, if you need to do it frequently, you probably have an app on your phone to convert for you...

BUT it's good to know how to do it, and if you're a homeschooling parent, you will (most probably) need to teach your chid to convert C to F and F to C in science and in math.  Of course there are the two normal formulae (with +32 or -32 and 5/9 and 9/5) but sometimes that gets confusing.

SO -- here I am today to tell you my favorite EASY way to convert between these two!  I learned this "trick" in college from one professor (which one? I have absolutely NO recollection!) and have used it ever since (and taught it to my kids).  I do wonder why it's not taught more!

Well, after all that build up, here's my method!

a) begin with the temperature
b) add 40
c) multiply by 9/5 or 5/9, depending on the direction **
d) subtract 40
e) be happy that you have done the conversion so easily!

**so how do you know which to multiply by?  Well, you know that the degrees Fahrenheit are higher (think 212 F=100C or 32F=0C) so if you are going from F to C, the number will be getting smaller, so multiply by the smaller fraction (5/9) and if you're going from C to F, you know it'll be larger, so you'll multiply by the larger fracthio (9/5)

That magic number, 40, makes it so easy!

Want to see an example?  Let's do the boiling point of water (212F or 100C)

Okay, let's go F--->C
212 + 40 = 252
voila! :)

How about the other direction?

What do you think?  I hope this makes your life easier! :) Just remember the fractions 5/9 and 9/5 and the magic number 40!


  1. Fascinating...I've never heard of that. I'll definitely be sharing with my son. He loves knowing things like that.

  2. Great little tidbit of information and something to teach my children, too!

  3. What a handy trick. I was in school when Canada converted to metric and was taught to double the C temp, subtract the first digit of the product then add 32 to find the F. They didn't teach us the opposite.
    So 10+10=20-2=18+32=50 (I already knew 10 was 50 so it works)