An Easy Way to Convert Celsius to Fahrenheit

7 May 2013 · 27 comments

-1, -2 = 29On our final night in London last month, Kim and I had dinner with Laura Roeder and her husband, Chris Williams. They were married in November, roamed the States while waiting for Laura’s visa, and are now settling in the U.K.

Laura’s from Texas, and though she likes the U.K., she finds some things — such as converting temperatures from celsius to fahrenheit — a bit confusing. Chris, who is from England, has similar trouble with temperature conversion, but in the opposite direction.

“I have a little trick that makes converting celsius to fahrenheit pretty simple,” I said, taking a sip of wine.

“Really?” said Laura. “It never seems that simple. You have to subtract 32 and divide by nine-fifths or something like that. It’s complicated.”

“He can just do it in his head,” said Kim. I had spent the last month converting temperatures for her while we traveled across Europe.

“What’s the secret?” asked Chris.

The Secret to Converting Celsius to Fahrenheit

“The secret is to memorize a couple of ‘landmarks’,” I said. “For instance, most people know that zero degrees celsius and 32 degrees fahrenheit are the same. That’s your first landmark. Zero celsius is cold. In fact, it’s the freezing point.”

My friends, their mouths full of pizza, nodded in agreement. That was an easy one.

“Well, there are just a few other landmarks you need to know,” I said. “The first is fifty degrees fahrenheit, which is ten degrees celsius. That’s a cool day, but not a cold one.”

“Next is 68 degrees fahrenheit, which is a comfortable room temperature. That’s twenty degrees celsius. Easy, right?”

“Well, it’s not too hard so far,” said Chris. “Fifty is ten. Room temperature is twenty.”

“Right,” I said. For the next landmark, reverse the 68 degrees to get 86 degrees. Thirty degrees celsius is 86 degrees fahrenheit, which is a warm day. Finally, a hot day is forty degrees celsius, or 105 degrees fahrenheit.”

“That lets you count by ten degrees celsius,” said Laura, “but what about all the temperatures in between? What about 26 degrees celsius, for example?”

“There you have to do a bit of math,” I said. “But only a bit. And you don’t need to remember any complicated formulas. Instead, just remember that 18 fahrenheit degrees equal ten celsius degrees. Naturally that means that nine fahrenheit degrees is five celsius degrees. Now you can count by fives. For smaller increments, just estimate that two fahrenheit degrees is one celsius degree. Does that make sense?”

“I guess so,” said Kim.

“You wouldn’t want to use this method for science,” I said. “But for daily life, it works just great. And though it may sound a little complicated at first, it’s really very easy.”

“Who taught you that?” asked Chris.

“Nobody,” I said. “I just made it up myself. I’ve been doing it this way for ten or fifteen years. And to be honest, I now find that I think in celsius instead of fahrenheit. It makes sense once you get used to it.”

Untitled
Kim and Laura and our enormous pizza…

How to Convert Celsius to Fahrenheit

Okay, in story form, this method might seem a little complicated. But it’s not. Let me give you a bullet-point summary:

  1. To begin, memorize five easy landmarks:
    • Zero degrees celsius is 32 degrees fahrenheit. This is cold.
    • Ten degrees celsius is fifty degrees fahrenheit. This is cool.
    • Twenty degrees celsius is 68 degrees fahrenheit. This is comfortable.
    • Thirty degrees celsius is 86 degrees fahrenheit. This is warm.
    • Forty degrees celsius is 104 degrees fahrenheit. This is hot.
  2. Next, remember that ten celsius degrees is equal to eighteen fahrenheit degrees. (It also helps to remember that five celsius degrees is nine fahrenheit degrees.)
  3. Finally, know that you can estimate that one celsius degree equals two fahrenheit degrees.

Actually, that last tip is key. If you really want to make things easy on yourself, that’s the only thing you have to remember: You can estimate that one celsius degree is two fahrenheit degrees. Then when you here that it’s 26 degrees celsius outside, for instance, double that (52 degrees) and add it to 32. In this case, you’d end up with an estimate of 84 degrees fahrenheit. It’s actually 79 degrees fahrenheit, but 84 is probably close enough for your purposes, right?

Thermometer photo by OliBac.

1 David May 7, 2013 at 10:09

After reading the first paragraph I was all geared up to school you on the “right way” to do it, but turns out your spot on.

Since I’m mostly using Celsius when scuba diving, my landmarks tend to be based on what water temperatures are cold, warm, hot. When living and working in New Zealand, though, this slipped over into air temperatures. You very quickly adapt to what the normal range of air temperatures are in your local climate.

For temperatures that are outside my range of landmarks, I just do a quick x2 + 30 (easier than 32) with a small error correction. I know that at 0C the error is essentially zero (2*0+30 almost= 32). I also know the farther away from 0C you get, the more error correction needs to occur.

So if someone told me, “quick, what’s 40C?” My head would go (40*2+30=110) then I’d subtract about 10 for error, which would give me 100, which is close enough. For 30C, I’d subtract about 5 to get 85 (again, close enough).

This is a good fallback for when landmarks fail you.

2 ldboomer May 8, 2013 at 05:32

This is also what I was taught to use while I was living in Europe

3 Mrs. Money Mustache May 7, 2013 at 10:33

Nice. That’s exactly what MMM taught me when we moved to the US. You guys will get along great. :)

4 SG May 7, 2013 at 10:43

Wouldn’t it be great if the USA would switch to celsius? (and, while we’re at it, to the metric system?)

Btw I have a similar routine for converting miles to kilometers. The factor is 1.609 (which is a bit simpler than the Fahrenheit/Celsius conversion) but with just two landmarks you can get by pretty well when driving in a miles-country with a km-odometer-car:
30 miles is 50 km
50 miles is 80 km

5 Linda May 7, 2013 at 11:01

Those are good landmarks to keep in mind. I used the 20 C/68 F and 0 C/32 F milestones when I was living in Canada all the time. Here’s another easy one to add: 39 C is the normal body temperature, which is 98.6 F. When I hear temps are over 30 C I think it is hot; when I hear they are close to 39 C I think it is burning up outside!

I found it more awkward adjust to weights. I always felt weird ordering 500g of something at the deli counter instead of just saying “half a pound of…” And in the UK, don’t they use “stone” when talking about the weight of people. That would totally blow my mind!

6 jdroth May 7, 2013 at 11:03

Actually, Linda, 98.6 degrees is 37 celsius. That’s a new one for me, and I like it. Thanks!

7 Elizabeth May 8, 2013 at 04:01

I used to work a deli counter and learned to convert pretty quickly :) Even though we officially use metric in Canada, many people still think in imperial. Myself included — I tend to think in inches and feet for short distances (probably because of my hobbies) but metres and kilometres for longer distances, for instance. I’d always give you my height in feet/inches and I measure my weight in pounds.

I have no clue what a “stone” is though! :)

8 Mike May 8, 2013 at 05:35

A stone equals 14 pounds, and it’s the most common way to express body weight in the UK and Ireland. So if someone asked me how much I weigh (170 pounds), I would respond 12 stone 2.

9 Malva May 7, 2013 at 11:30

That’s an interesting way of looking at it. It’s more precise than my “*2+30″ method.

10 Scott May 7, 2013 at 11:40

Double the Celsius number, subtract 10% and add 32 to get the Fahrenheit number.

11 Chrys Hansen May 7, 2013 at 21:47

This solved the conundrum for me, but then the article would have been a lot shorter and probably no pizza.

12 bethh May 7, 2013 at 13:20

I’m either confused, or you made a mistake, or both. First you say:
Ten degrees celsius is fifty degrees fahrenheit.

Then you say:
remember that ten degrees celsius is eighteen degrees fahrenheit.

Since you also say:
(It also helps to remember that five degrees celsius is nine degrees fahrenheit.)

I think you mean:
remember that two degrees celsius is eighteen degrees fahrenheit.

In which case I’m tracking a bit better!

13 jdroth May 7, 2013 at 14:05

Beth, you’re confused — but it’s because of my poor writing skills. ;)

Let me go fix that.

14 bethh May 7, 2013 at 15:17

You’re right – whatever you changed helped!

15 Anon May 7, 2013 at 16:01

Thanks for the tip, but actually, it’s a common myth that the UK has gone totally metric. Fahrenheit is still used fairly often here for summer temperatures, but winter temperatures are usually in Celsius because of the convenience of zero being freezing point. We also still use miles, pints, feet, inches, stones, pounds etc. in plenty of daily life situations.

16 Mike May 7, 2013 at 17:37

I’ve gotten pretty good at counting by 18 for each 10° but for the general feel, one of my teachers back in school taught us this rhyme:

30’s hot,
20’s pleasing,
10’s not,
And zero’s freezing.

17 Greg May 10, 2013 at 07:04

This is similar to what we used while on vacation in New Zealand.

Zero is freezing,
10 is not,
20 is warm,
30 is hot.

Worked well enough for us for determining how many layers of clothes to wear.

18 moom May 7, 2013 at 21:15

Yes, this is what I have always used.

19 Julia May 8, 2013 at 05:47

Years back, having moved to Canada from the US because I married a Canadian, I needed a quick way to get used to Celsius. Easy, a few markers:
0C = 32F
10C = 50F
28C – 82F
And whatever falls in between you have a rough idea of how warm or cool it will feel.

And the easy C -> F conversion: Double it, add 30, take off a few = rough F.

20 Andrew Snyder May 8, 2013 at 06:35

Celsius and the metric system may be more rational, but they contain no poetry, and they have no soul.

21 Robin May 8, 2013 at 08:32

I go by this flip
28 = 82
It’s an estimate 82.4, but gets you in the “is it HOT or nice” arena quickly.

22 Lan May 9, 2013 at 08:12

The easiest method is this, we’ll use 27 C

1. Double it: 27 x 2 = 54
2. Subtract 10%: 54 – (54 x 0.1) = 54 – 5.4 = 48.6
3. Add 32: 48.6 + 32 = 80.6 F

23 Bon Crowder May 10, 2013 at 18:10

The niftiest thing is that the linear equations (the lines that relate F to C and C to F) intersect.

In English that means that -40 degrees is the same in either temperature scale!

(But really – who wants to be in -40 degree weather to begin with, right?)

You’re tempting me to write about this!

24 Olivier Bacquet October 2, 2013 at 21:21

Hi,

Could you give me credit for the photo in use in that post?

Photo credit: ©Olivier Bacquet / OliBac
http://www.flickr.com/photos/47757737@N00/2983779842/

Thank you,
Regards,

Olivier Bacquet

25 jdroth October 3, 2013 at 06:12

Sorry. I’d given credit at the end of the article (as I always do when I use photos from Flickr), but malformed HTML was preventing it from being seen. Should be fixed now!

26 Olivier October 3, 2013 at 10:20

Don’t worry, it’s OK !

27 g llewin January 22, 2014 at 09:23

i have a little ”jingle” which i use for quick reference.
have you noticed how newspapers tend to use a ”celsi-heit”
scale, where cold snaps are bemoaned with BELOW ZERO
and heatwaves with PHEW! 90 IN THE SHADE!
why? they look dramatic. i just hope vistors are aware of
this tabloid tendency

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