A Little Trick for Converting Centigrade to Fahrenheit

Neat, I like it.
Now, there is a temperature at which the reading (degrees number) is the same in -both- centigrade (Celsius for us old timers) and Fahrenheit. What is that temperature???

regards - tom
ps - not a trick question, for real. Hint - it would be feel cold.

Just between us old timers, that would be -40.

Best, Steve

How nice that that works for you, sdb. However, with all respect, anyone who can do the arithmetic in your "shortcut" ought to be able to do the arithmetic to get the actual value. Also, your shortcut needs to include the notion that the Centigrade temperature must be expressed as a 2-digit value -- if you're using your formula to "convert" 4C to Fahrenheit, you need to think of the doubled 4 as "08," and thus subtract 0 (not 8) before adding 32.

The shortcut is actually calculating a value for Fahrenheit that's equal to (1.9C + 32), rather than the actual (1.8C + 32).

And I did not write this reply to be informative, but rather to show off that I passed algebra class several years ago, at Newton High School.

Rizzuto, Newton High apparently has done an excellent job.

Yes, what you say for Centigrade values 1-4 is correct. I assumed the zero was intuitive but we all know about assuming. One must also remember that when working with minus values that minus a minus is a plus.

The tip I offer is meant to allow the calculation, in one's head, in a matter of a few seconds and to arrive at a Fahrenheit value that is, if not exact, useful as a reference---to those ends I believe it's helpful. My hat is off to those who can easily in their heads work 9/5C + 32 or 1.8C + 32.

Best, Steve

9/5C or 1.8C - have no idea what this even means, so unless it's a test, do I really care whether it's 74 or 78-degrees? Don't think so.

Take the C, double it and add 32... close enough.

23C x 2 = 46 + 32 = 78... 4/degrees won't make me change what I'm wearing.

When it's hot, it's hot; when it's cold, it's cold... and you know it. Anything in-between doesn't much matter - it's comfy!

All this show that the US really missed the boat when they failed to go metric in the last century.

this is making my head hurt--better idea, just bring a thermometer with you I have a tiny one on a keychain which hooks to my purse, and also my alarm clock has one built in!

but @NoFlyZone is absolutely right, we are clueless in the US about metric. I have also printed up cheat sheets to convert cm to inches and made them into bookmarks to put in my bird guide, because all the sizes in the guide are listed in centimeters!

nofly - i have to agree. I wish we'd gone metric back when it was being talked about. I was in junior high at the time and probably could have made the shift, although even then it would have been tough. Now (as an old dog) it would be much harder.

and sandi - the shortcut i always heard is to double the number and add 30, rather than 32. I think it gets you a little closer. Still not quite accurate, but as you say, close enough for what most of us would need.

althom - 30 also works for me.

Metric/schmetric... anything with a decimal point will further mess me up! Numbers/Me = dense! Unless there are lots of "Benjamins"

I always double it and add 30. The math is a little easier that way.

The same works in reverse for our non-American friends when you come to visit. If the temp is 70°F, you can subtract 30 and divide by 2. Hence the temp in Centigrade is 20°C.

I remember in the 70's when we were learning the metric system and they were telling us we will switch someday soon. I wish that had happened but somebody must have dropped the ball on that.

Metrics are used in science and medicine here in the US, and to the best of my recollection that has always been the case.

Okay let me get in on this !

To show that -40 C = -40 F :

F = 9/5 C +32
then we have

5F = 9 C +160

But since F has to be equal to C we have

5F = 9F +160
-4F = 160
F = 160/(-4) equals -40

So at minus 40 both C and F are equals ( Brrrr !)

Excellent Percy, you get full credit for showing your work!!!!
Now for EXTRA credit - why is that fraction 9/5, 9/5C?????

regards - tom

I immigrated in 1966 to the US. I never bothered to learn the US system of Farenheit and inches, because I was told that we (the US) would switch very soon and be "equal" to the rest of the world!!! Yeah, right .... I'm still waiting and I'm still ....

Clueless in Seattle!

Thanks cary999 !!

Reminds me of the old University days...."full marks for showing all your work" and "2 marks out of 10 for only the correct answer."

safarimama:

I have never gotten used to the metric system.. You cannot teach an "Old " dog new tricks.

When I see a distance in Europe or Canada that reads 90Km , I quickly multiply by .6 to get 54 miles. !!!

You're most welcome. But you're not going for the EXTRA credit Percy??
Anyone?...Bueller?...Bueller?... Anyone?
Ok, a hint then. 9/5 is the simplification of the original fraction which is 180/100. Why it is 180/100 well be good enough for the EXTRA credit

regards - tom

Metric is so easy; everything divides by 10 or 100.

How many inches in a foot? How many feet in a yard? What the he...ll!!!

Percy, what's there not to get used to?

tom: 180 and 100 are the number of degrees, in F and C respectively, to go from the freezing point of water to the boiling point.

As for metric vs English system, it boggles the mind that the U.S. remains a 3rd world country -- in fact, the world's only 3rd-world country -- in this respect. Not only is our weird little system difficult to calculate, it is profoundly confusing to most people. Especially the very bizarre notion that the word "ounce" has two entirely different meanings. So 1 ounce of pea soup does not equal 1 ounce of pea soup.

In my travels I have developed a "feel" for kilometers, so I don't need to convert them. But for temperature, I haven't been able to develop a feel, so I do what's described here, with a slight difference. I double the Celsius number, subtract 10% (that's where I differ from others) and add 32. That's close enough to let me know whether I want a swim suit or a snow parka.

Now, for extra credit, who can explain the difference between Centigrade and Celsius, and tell us why one term is preferable in some situations, and the other in others? (Not me, I'm clueless on this one.)

Celia

rizzuto - well done lad!!!!
So the 180/100, 9/5, is the scale conversion factor and the 32 is because F scale starts freezing at 32.

Having a BS in physics and engineering I learned the cgs/metric years ago and wished the USA had followed thru on our half hearted attempt to convert in 1975(?). I know believe we will and are, just going very slowly.

regards - tom

Sandi, jczinn - read no further

Celia, according to an article in USAToday, "The Celsius temperature scale is still sometimes referred to as the "centigrade" scale. Centigrade means "consisting of or divided into 100 degrees." The Swedish Astronomer Andres Celsius (1701-1744) developed the centigrade scales for scientific purposes. It has 100 degrees between the freezing point (0°C) and boiling point (100°C) of pure water at sea-level air pressure. An international conference on weights and measures voted to name the centigrade scale after its inventor in 1948." In addition an article in Science said that at the international conference in 1960 the scale was defined in a way that makes the adjective centigrade inexact.

And---but I'll need Rizzuto and Tom to weigh in/confirm this---your approach of taking 10% of the doubled Celsius temp is more than just close enough: it gives you exactly F = 9/5C + 32 !

Best, Steve

You're exactly right, Steve. Celia's method of doubling the Celsius/Centigrade temp, subtracting 10%, then adding 32 is another way of calculating (expressing) the F = (9/5)C + 32 formula.

>>>Metric is so easy; everything divides by 10 or 100.

>>>How many inches in a foot? How many feet in a yard? What the he...ll!!!

>>>Percy, what's there not to get used to?

Safarimama - it's not the math that takes getting used to. It's having a sense for the meaning. I know how 70 degrees F feels because I've grown up knowing. I know I need a jacket for 50 and a winter coat for 30. And if it's 80, short sleeves are perfect. But 20C? It's meaningless to me. Ditto for feet and miles. I know how long it takes to walk a mile or drive 10 miles. I don't have the same feel for kilometers - I have to do the conversion .6 conversion in my head. It's the "feel" for temperature and distance that is hard to adjust to. I think it must be like learning a new language - beginners can look up words and translate. But you have to practice a long time to get to where you can actually think in the new language. Hope that explains it

well safarimama,

When you were totally used to miles feet and pounds and then you get the metric system, you only think it is mentally easy !~

let me give you some examples

1.If some asks me to raise my hand to a level of 5 feet , 7 inches... I can come pretty close.

Tell me to raise my hand to a level of 142 cm ....I would only be guessing ,as I try mentally to convert to feet and inches.

2.2 pounds = 1 Kilogram, so when you go shopping you buy meat that is $4.20 per Kilogram (is that a good deal)

I am happy to see Tiger Woods hit the ball 325 Yards, I do not want an announcer telling me Woods just hit the ball 296.95 meters.!!!

We had a big rain storm !!! it rained 38 millimeters !!!, now spread your thumb and index finger to 38 millimeters !!...not easy is it.!!

Now 38 millimeters is 1 and a half inches! ( okay ,okay it is 1.496063 inches to be more exact.

Now you can spread your fingers to 1.5 inches very easily.

If you can easily know just how high 117 centimeters is

and that a football player just just made a 17.2 meter catch.....you way ahead of me

Oh yes,I majored in Math and Physics, so I do know all about the mertic systems.

I can remember having to calculate Forces in Pounds and then converting that into Newtons...or dynes

I can tell you that I would rather some tell me that the pressure is 10 pounds per square inch....then to tell me that the
pressure is 68,960 Newtons per square meter.!!!

Your better than I am by a mile if you can handle the metric system, if you come from a non-metric country !!!

althom 1122

You are Right on , I could not have said it better.

I have no feel for 37 Kilometers but I do for 37 miles.

If if sterak is $7.00 /pound , I have a feel for that.

If steak is $14.30/ Kilogram , I do not want if that is a good deal.

When the weather man tells me it rained 8 inches over the past 2 days and floods are everywhere.....I can feel that.

If he said is rained 78 millimeters.??? what is that !!

Thanks for saying what I wanted to say, in a better way than I could have !

Percy - well said.

I'll stick with what I know and the few things I've figured out to get thru metric environments.

Anyone who grew up in the 70s, knows that a Kg is 2.2/lbs.

For Kilometers, I just subtract 1/3rd and know my distance or speed.

And, 3.5/ltrs = 1/gallon.

When it comes to temperature, I know cold, hot or warm... the exact degrees - who cares.

I can go about doing most anything to get me thru and not break the law!!!

OK, I stand corrected; I was only thinking of how easy the metric system and Celcius is to figure.

Being born and growing up in Sweden, the land of Celcius, living in the US for the past 20 plus years now, I have a "feel" for both Celcius and Farenheit. That wasn't as difficult to aquire as you make it sound. Just give it a year and you'll be a convert.

However, but to be honest, I still don't know how many inches in a foot, how many feet in a yard or ounces in pound etc. That makes totally no sense at all to me. I never got a feel for that. It's just totally impossible to remember.

I also miss the 24 hour clock!!!

Recall when my brother first moved to Canada, the first snowstorm when the weather person said their were XXXcm of snow... he had to ask his students how much that was. To him anything that didn't inhibit his driving was perfectly okay, whether inches or cm. And, after 25/yrs up north, he's just getting the hang of it... and to think that he teaches math. Poor kids! Ha! Ha!

Hi sandi and Hi safarimama :

Well you would think that if a person grew up with the metric system, then pounds and inches and feet and miles would be foreign to them !!?

Not so!

Canada converted to metric in the early 1970's and people still do not like it.

The government tried to force it upon everyone quickly by having "Metric Police" going around making sure that grocery stores and public places were using metric.

My nephew was born the early 1980's and he took metric in school....had to ,there was no choice.

But to this day when he asks me about distance he used miles.

He would not ask me , for example, how many Kilometers from Los Angeles to Palm Springs, but rather how many MILES is it .

In fact, if I think about it , not one of my Canadian friends has ever talked to me in metric, no matter how old he is !

In my humble opinion they should have used metric for science when neeed,or for international trade when need, but left pound/yards/miles alone.

Oh yes, Canada thought their trade would boom internationally when they converted to metric....

A government study later on proved that was not the case.

I am very pleased that the USA has not gone metric !!

Good Night ladies. ( bedtime sandi )

Oh yes I forgot to mention it safarimama!,but I LOVED Stockholm.

What a gorgeous place to visit and walk around.

The views from the City Hall Tower back onto Gamla Stan are just terrific.

Okay now for sure Good Night Ladies ( sshhh sandi is sleeping already) .

Miles!????!!! Oh yes!!! Don't know anything about growing up in Canada, but .... One Swedish mile is 10KM!!!

What are you talking about? I consider one mile to be just that -- 10km. I have no idea how many yards is in an English mile? Do you or anybody?

Does it mean anything?

I drive a Volvo, so when in Canada (to visit LyndaS), it's easy to compare. 100KM is 60 miles (American). It's on my speedometer!!! Easy enough for me. I'm blond (or used to be). I get a "feel" for it then. Just don't ask me to convert it, pleeeeeease!

I find it fascinating, "Percy," that you opine confidently about what the Canadian people do or don't like, yet you are apparently not Candian.

I travel to Canada regularly and interact with people in our offices in Canada daily, and I have yet to hear anyone use anything other than meters and grams for distance/weight.

I guess I also find it disheartening that some people seem to actualkly exult in their ignorance: "I'm proud of knowing nothing about the metric system." In almost any other culture I know of, people would not boast of their ignorance, and maybe they'd make the effort to remedy that ignorance.

I mean, really, there's nothing about the metric system that 95+% of the American public could not master if they wished to take the time to learn it. Well I can understand if someone says that they choose not to take the time to learn about the metric system -- they're certainly entitled to use that time doing something else (working, learning about something else, watching soap operas, whatever). But to wave the flag of ignorance and proclaim it gladly to the world -- that seems unfortunate.

I love that trick, thanks.

As Henry Ford said
"Why waste my time when others can do it for me"
Use a cellphone

rizzuto

I happen to know that Percy IS Canadian ,born and raised in Canada.

He is a good e-mail friend of mine and I am also Canadian.

We all grew up with the Imperial systems and when Metric was forced on us , we all learned it , we did not like it but we learned it.

I know the Metric system very well and I NEVER use it and none of my friends use it.

We mentally convert in our minds.

For you to call Percy ( a very well educated man) ignorant , is insulting .

Percy said none of his friends use the metric ( and frankly none of mine do either), but we all can use it and we know the metric system well.

Don't be calling a a Canadian a non- Canadian and ignorant

for giving his opinion about the Metric Systems.

I am offended for him and all Canadians.

Thanks, Steve, for the Celsius/Centigrade info!

Celia

What surprised me when visiting a friend in England, driving the highways and seeing the speed limits posted in miles! Duh! Their odometer though was is both miles/km.

Seems there's a mix-n-match, some places.

Ok, so , what is the "little trick" to go from Fahrenheit to Centigrade? That is converting 80F to 27C?

regards - tom
ps - I don't know one as easy as going the other way

Gosh , Gee , Thanks jmvp.

How are you doing. Been anywhere recently since coming back from Egypt. ?

Thanks again, but that's okay, rizzuto is entitled to her opinion.

cary999:

I have to apologize ,as I missed your question about why the fraction is 9/5 C

Okay let me take a stab at it and you can correct it,as it has been a while

On the Centigrade System, water freezes at 0 degrees
and it boils at 100 degrees.

On the Farenheit System water freezes at 32 degrees and boils at 212 degrees.

Therefore to change from 0 C to 100 C is equivalent to a change from 32 F to 212 F

Therefore 100 C change in units is = 180 F change in units.

I know,I know , some will say ( not you cary ) that

100C is NOT = to 180 F !!
But yes it is because you are moving from 32F to 212 F , which is 180 units.

Dividing 180/100 = 9/5

You probaly have a better method cary !

Thanks Percy, you did outstanding work showing -40C equals -40F. But you are about a "day late and a dollar short". Rizzuto already answered. However, once again you show your work!!!! So you still get a big "thatta boy"!!!!!

regards - tom

Celia, you're welcome.

ann_nyc, glad it works for you.

Tom, I was afraid you'd ask how to go the other way. I think
P_M had a decent approach, i.e., substract 30 and divide by 2 (but I think if you add 2 to your answer you'll be almost spot on--without it the answer the approach gives appears to be 2 too low). 80 - 30 = 50 ÷ 2 = 25 (+ 2 = 27).

Steve

Guess I missed P_M's subtracting 30 and divide by 2. That's probably as easy as we're going to get it. P_M's going C to F of taking C multiple by 2 and adding 30 is also easiest. Think I'll use those two for everyday weather temp. Thanks P_M.

regards - tom

cary999

Gosh darn ,I did want those "Extra" credits

Here's how I do it:
http://metricconversioncharts.org

print it out and take it along when travelling; easy!

You are most welcome Tom.

Well, so, as a Canadian I just feel compelled to weigh in here (in lbs not kg)

I am, probably like Percy, one of those boomers that got stuck in the middle - we grew up learning lbs, miles, farenheit. We knew that as a teenage girl we should only weigh 125 lbs max, that driving with our friends down the highway should only be 60 mph - or well, Ok, we stretched that one a bit. And that we needed to be in bathing suits at 95 degrees, t-shirts & shorts at 80 degress, a jacket at 60 degress, a winter coat at 30 degrees, and at home watching TV at 40 below farenheit (yes, I'm from the prairies).

Then, suddenly this guy stands up & says, no wait, we should be on the metric & by golly we will not let any products into our country unless it is in grams not oz - and oh by the way it also has to be in French too.

So, as adults (or semi-adults maybe) we all tried very hard to learn the metric system. We cheered our kids on when they came home from school proudly displaying that they knew the metric system, but also secretly smiled when they talked about inches instead of cm - must have learned that too we thought!

But, Percy is right - we may have learned the metric system - or some parts of it, but we still use imperial measures in day-day things. Most of us are fluent in both temperatures, and driving - but most of us still couldn't figure out without converting whether we should build our decks with 4" boards or whatever the metric conversion for that is. Or - a perfect example from Percy above - I wouldn't have a clue as to where to raise my hand to 142 cm.

I learned temperatures by feel because it was really easy & we never hear the temperature on our news in anything but celcius. It became very easy to adapt to know now you need the bathing suit for 40 degrees, shorts & t-shirt for 30 degrees, a jacket for 15 degrees, and a winter coat for 0. And - oh yes, we still stay inside when it's 40 below when we visit mom in the prairies in the winter.

Driving was easy too, because we just HAD to get used to it, and besides most cars we buy here still have both km and mph on them, so you can always drive that way if you have to. And because we got the feel for driving, we also came to know it was too far to walk 10 km to go to your friend's house, best to get in the car.

But cooking in grams & kg and still boggles us - at least us older folk. For one thing, most of my cookbooks are either from the US or I've had them a long time, as they are in imperial, not metric. My measuring spoons say both, so it's easier to keep to the old system. And no matter what the package says a litre of milk will always be a quart of milk and if I get more - or less than I am expecting, I can't tell the difference.

And when one goes to a quilt shop, one still asks for 3 yards of that material. The sales girl rolls her eyes & says, sorry ma'am, I need it in meters, not yards. So I say, well OK then give me 3 meters and she does a little happy dance because she has now sold me more material than I need because I can't convert the darn measurement!

And same with weights. Someone tells me they weigh 67 kg, I say OK, should you diet or eat more french fries ? I have no feel for it.

Funny thing is, our kids - even though they learned both - seem to use the same ones as us. My son, just into his thirties, certainly learned the metric system, but still talks in inches & feet and lbs and ounces. But talks temperatures in celcius and distance in km. Guess we parents are more influential than we think! Either that or the teachers never really pushed the metric system either.

Great info and done with a sense of fun. Stumbled in here and read the back and forth with a smile! I almost bought a kilo of sandwich ham in Mexico a few weeks ago. I never buy 2.2 lbs. of sandwich meat. I stopped the sales girl. She was in a hurry to give me a kilo. I ended up with 1/2 a pound before I could stop her. I turned to my friend and we had a laugh. The sales girl thought we would assume we were getting a pound. Just goes to show that when traveling, one must have some understanding of the metric system or pay the price.

Thank you LyndaS not because you agree with me but because of the lovely story you told.

I can identify with everything you said,and you said it well.

I remember that none of us wanted the Metric System but our beloved Prime Minister of the day , knew what was best for us all.!!

I have been converting ever since the Metric system arrive .)

I was in Germany last year and when I reading the mileage ( oops Kilometers) on a highway sign ,saying 37 Kilometers to Dresden........... my mind quickly went
hmmm! 37 Kilometers, make that 40 Km.(because 40 is an easy number), now times 0.6( for the conversion) equals 24 miles , so just a few miles under 24 miles to Dresden.!!!!

I am sure many of us do it instinctively ,it's become second nature !!

Thanks again for the lovely story (PS ,I did not want to mention the French part, but I am glad you did .

I have a HEADACHE!!

SD

...well, as long as your temp's 37C