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Converting Celsius temperatures back to the Fahrenheit scale

Hi World Travelers,

Do you convert the weather Celsius temperatures back to the Fahrenheit scale using your calculator?

As strange as this may sound, I mentally do the conversion using the casino dice table layout. This works very well for the everyday-life temperature range of 0-50C which is 32-122F.

Or Cx2+25 to get a rough F...

Posted by
69 posts

30 is hot, 20 is nice, 10 is cold, and 0 is ice?

Posted by
5504 posts

Like Jone but expanded:
40C = Hot
30C = Warm
20C = Comfortable (shirtsleeve/T-shirt weather)
10C = Cool (Sweater/fleece weather)
0C = Cold (Jacket weather)
-20C = Very cold (Stay inside)

Posted by
11431 posts

Edgar 40 is death !!! I die over 30 ! Where did you grow up ??? Death Valley ? Lol

Posted by
8293 posts

Multiply centigrade temp by 2 and add 30

Posted by
11431 posts

Vic , being Canadian I don't convert anymore , I used to as I grew up with Fahrenheit , but now decades later I do just think in Celsius , finally .

I like the conversion that Jone posted .

Posted by
5504 posts

Pat: Rounding off. 40C = 104F, but yes 40C is hotter than 38C (100.4 F). Here in Medford (OR) we kept below 100F several summers ago but last summer hit something like 109F for a day or two.

Posted by
4637 posts

Celsius makes much more sense than Fahrenheit. 0 degree Celsius - water start freezing. In Fahrenheit that happens at 32.
100 degrees Celsius - water start boiling (at the sea level - in higher elevation it boils at less than hundred). In Fahrenheit that happens at 212. 0 degrees Fahrenheit is minus 18 Celsius. If you don't have a converter just a calculator (or pencil and piece of paper) then multiply Celsius times 1.8 plus 32 and you get Fahrenheit. Example: 30 degrees Celsius times 1.8 = 54 and add 32 = 86 degrees Fahrenheit. I don't understand why we are the last country still left on this archaic system and why we don't join the rest of the world.
I want to give one example of this mess: when I still worked we measured patient's temperature in Fahrenheit but temperature of the air patient was breathing from his ventilator was in Celsius. Maybe thermo-probes were made in China :-) . OK, one more example: several years ago our space sond crashed on the surface of Mars because some values were programmed in metric and some were in our archaic system. I think keeping non-metric system costs us a lot of money.

Posted by
17657 posts

I like a modified Edgar scale. I start by knowing that 0°C = 32°F and 20°C = 68°F (that's standard atmospheric condition or room temp. Every science student knows that.). For every 10°C difference add or subtract 18°F. So,

0°C = 32°F
10°C = 50°F
20°C = 68°F
30°C = 86°F
40°C = 104°F

If you want a little more accuracy, pick the nearest 10°C increment and add/subtract 2°F for every 1°C difference. For 16°C, start with 68°F and subtract 8°F (2 x 4°C). That gets you 60°F, which is within 1° of the actual answer, 60.8°F.

As for doubling the °C reading and adding something, I would prefer adding 28°F because that makes the conversion right on, 68°F, at room temperature (20°C).

And remember, if the readout is in deg C. It's actually ±0,5°C, or ±0.9°F, or only accurate to about 1°F anyway. Most of these estimates aren't that much farther off.

Edgar 40 is death !!! I die over 30 ! Where did you grow up ??? Death
Valley ?

A high temperature of 104F is not unusual for a summer day in Denver. But I grew up in Seattle, and there, with the humidity, 104F would have been very uncomfortable.

Posted by
607 posts

"It doesn't matter what temperature a room is, it is always room temperature."
- Steven Wright

Posted by
2075 posts

Thanks, Jone, for your poem. That should be really easy to remember. I don't know why I can never remember the Cx2 + 30 formula.

I just can't stand that the US has never converted to the metric system. I can remember learning the metric system in school in the 60s. We were taught that the US would probably be converting at some point. But we still haven't done it! It's insane.

Posted by
2731 posts

I find all the negative temperatures in Celsius impractical, but then I guess it depends upon where you live. I'd go for the true international scale, Kelvin! No negative numbers, eminently practical.

F: ...-30.......0.......30......60.......90

K: ..239....255...272...289.....305

Posted by
4637 posts

Why, Tom? It's pretty practical. When is minus it means that is freezing. More degrees minus, more freezing. With Fahrenheit you need to know that freezing starts at 32. With Celsius easy - above zero - not freezing, under zero - freezing. Zero to hundred degrees - water, above hundred - steam.

Posted by
12103 posts

On the conversion between C and F: I just know the important ones by heart. Now, 25C is 77F, 10C is 50F, 38C is 100F, etc. If I need more, I look it up in my list in the note book. Traveling between early summer to peak season, 18C to 33C, I really don't need to be that specific in a practical sense, either it's hot or hotter, 25C or 33C, etc.

Posted by
2731 posts

Because for some places, the temperatures can be negative for months at a time, 24 hours, in the C scale.

Posted by
2045 posts

The exact conversion is so easy to do in one's head: Double, subtract 10% (i.e. move the decimal point to the left and subtract it from the doubling, and add 32.) This is the easy mathematical simplification of the formula Celsius times 9/5 and then plus 32 = Fahrenheit.

Posted by
4637 posts

9/5 plus 32 to get from Celsius to Fahrenheit translated to common English would be Celsius times 9 divided by 5 plus 32 or as I said before times 9 divided by 5 is the same as times 1.8, e.g. Celsius times 1.8 plus 32 = Fahrenheit.

Posted by
4637 posts

Yes, Tom, but very few people live in those places and with global warming it will be even fewer. Kelvin is precise but not too practical.

Posted by
2731 posts

??? At least 300 million people live in such places.

Also, Kelvin is the scale of science and the SI standard unit for temperature, Celsius is just another throwaway household scale like Fahrenheit.

Posted by
6543 posts

Sure Celsius makers more sense, however my thought pattern is ingrained in Fahrenheit. At least F. is a little more precise. I pretty much ignore temperatures for the most part when out of the U.S.

Now if I could get over kilometers vs. miles.

I always know how much I'm spending for gasoline (in U.S. gallons and U.S. Dollars) when traveling Europe. It's 2.78 times 1.05 times .615= cost per mile in U.S. dollars and gallons. Right now, it's around $4.35 per gallon in Germany and around $4.65 per gallon in Italy for petrol. I've seen fuel twice that previously.

Posted by
4637 posts

Kelvin was derived from Celsius, e.g. difference in one degree Kelvin is the same as difference in one degree Celsius.
Tom, three hundred million? Not even 30 million. Not even one million. In southern hemisphere - Antarctica- nobody permanently lives. In northern hemisphere few people live in Alaska, northern parts of Canada, Norway, Sweden, Finland, Russia. Those are very sparsely populated areas.

Posted by
8889 posts

30 is hot, 20 is nice, 10 is cold, and 0 is ice?

I too like Jone's scale. When I was a child (in the UK), they used Fahrenheit (°F, aka degrees Fred Flintstone), they taught me °C in science at school, since I have been an adult nobody uses °F and I only think in °C.

If you want an exact conversion (no calculator required, you should be able to do this in your head):
°F = (°C ÷ 5 x 9) + 32

Posted by
4022 posts

Here's another simple chart:

28 C = 82 F
16 C = 61 F
04 C = 40 F

And for me, 20 C is NOT comfortable. I start relaxing at about 27, and prefer 30+!

I always know how much I'm spending for gasoline (in U.S. gallons and
U.S. Dollars) when traveling Europe. It's 2.78 times 1.05 times .615=
cost per mile in U.S. dollars and gallons. Right now, it's around
$4.35 per gallon in Germany and around $4.65 per gallon in Italy for
petrol. I've seen fuel twice that previously.

Of course in the U.K., we sell petrol (gas) by the litre but we measure road distances by the mile - and everyone still thinks about car economy in terms of miles per gallon.

Posted by
6047 posts

I don't convert Celsius temps back to Fahrenheit. On the contrary I convert Fahrenheit temps to Celsius whenever I go anywhere in the world other than the US. We seem to be the only country left living in the dark ages.

Posted by
11431 posts

Jane is it hot (over 30) regularity where you live in the summer ? I start to feel heat sick over 27 or so , over 30 I stay inside in ac .

We are going to Mexico this June and I am fraaking out about how I will deal with the heat . I anticipate spending most of my time in the ocean ( not pools they get too hot for me ) or in our room !

Posted by
5504 posts

If you want to be more nuanced in air temperature vs comfortable temperature you need to consider the air temperature and relative humidity. One measurement combining both is the "heat index". While it can get hot air temperature wise here in the southern interior valleys of Oregon our summer air is relatively dry during the hottest time of the day and evening.

On the other end of the temperature spectrum, wind chill is an important consideration. An air temperature of -10C and still air isn't to bad properly dressed. Skiing into the wind at -10C can be brutal.

Posted by
1834 posts

The USA must be the only country left in the entire world that still gives its weather forecasts in Fahrenheit!

Posted by
607 posts

I live in Canada and i recall changing over from imperial to metric about 40 years ago. So much easier to just divide and multiply by 10 and not having to figure out how yards in a mile, ounces in gallon etc.
But, after all these decades, we still buy our hamburger and apples by the pound.

Posted by
5316 posts

The only conversion I remember is
-40° C = -40°F
(which my daughter experienced spending a school year in northern Finland)

Posted by
4022 posts

Hi, Pat: Yes, we are regularly over 30 in the summer in our part of the country. In fact, much of July and August we hover around - or pass - 35. As it happens, I love it. And we (DH and I) don't have a/c in our house. It's not as bad as it sounds; our house was built long before a/c was available, so it was designed to be more comfortable in the summer heat than anything built since 1960.

And when it gets too much, we can always pop into a grocery store or library for an icy blast!

Good luck on your Mexican trip. My brother and his wife go regularly and love it, but they are also heat lovers.

Posted by
17 posts

Hi Everybody,

Yes, it seems that while traveling, there are many ways to convert the Celsius temperatures back to the Fahrenheit scale. Some are easier to do and remember than others while some are more accurate than others.

I thought that by this time, the U.S. would be on the world metric system instead of clinging to the old system of miles, yards, feet, tons, pounds, ounces, gallons, quarts, pints, etc. and of course Fahrenheit.

Some day we will join with the rest of the world, hopefully in our lifetime...

Posted by
4637 posts

To be more accurate where Fahrenheit temperature is exactly the same as Celsius is minus 42 degrees.

Posted by
8889 posts

Ilja, -40 °C/°F IS the cross over point.

°F = (°C ÷ 5 x 9) + 32

So if °F = °C (same value in both systems). Using basic school algebra:
°C = (°C ÷ 5 x 9) + 32
°C - 32 = °C ÷ 5 x 9
°C x 5 - 160 = °C x 9
-160 = °C x 4
°C = -40

I am amazed so many approximate formulas have been quoted in this thread. °F = (°C ÷ 5 x 9) + 32 was what I was taught at school, and I don't think either scale has been changed since then!

P.S. there is an old thermometer near where I work in a square with 3 scales on it, °C, °F and °R. R = Réaumur, freezing and boiling points of water are defined as 0°R and 80°R degrees respectively. This is another old defunct scale.

Posted by
4637 posts

Chris, it is indeed minus 40 when Celsius and Fahrenheit are equal. I must have read it somewhere and did not do my homework. When using calculator it is faster instead of 9/5 to use times 1.8 and instead 5/9 use divided by 1.8 so the equations are:
F = C x 1.8 + 32
C = ( F - 32 ) : 1.8

Posted by
17657 posts

I actually use the method described by Elkins Park Larry. It's exact. However, unless we are keeping records, it doesn't really matter to people if it's 73°F (or 72°F or 74°F), and the calculation is complicated for most people. Anyway, most of the time you see the temperature in °C express as a whole mumber, which is only accurate to half a degree C, which is almost a full degree F, so approximations that get you to with a couple of degrees F are close enough.

And, Nancy,

We seem to be the only country left living in the dark ages.

There is nothing dark ages about measuring temperature in degree Fahrenheit. In fact, it could be argued that the Fahrenheit system is superior because the graduations a smaller.

We call it the "English System", but the English no longer use it. We do, so let's call it the "American System". And the word "metric" simply means a system of measurement, so our system is a metric system, too. The so-called metric system, or SI, was invented by the French, so we should refer to it as the "French System". So, what do you want to use, the good old patriotic American system, or the alien French System.

To quote Mark Twain, "It is un-English, it is un-American; it is French."

Posted by
4637 posts

Lee, I would call it Old Patriotic system but certainly not good and good alien French system. I tell you why: it makes sense and it's much more practical. For example: there is 10 mm in one cm, 10 cm in one decimeter or 100cm in one meter, 10 decimeters in 1 meter, 1000 meters in one kilometer or 100 thousand cm in one kilometer or million mm in one kilometer. Now in real life - for example: you go to buy maps and they have scale. It's very easy to figure it out: when I go for a road atlas I want it in scale 1:100000 that means 1 cm on the map is 100 thousand cm in reality. That does not tell you much but cover five zero and you see 1 cm on the map is 1 km in real life. Try to do the same with "good" old patriotic system and you would soon find out which system is better. The same milliliters (ml), centiliters, deciliters, liters, hectoliters, milligrams, centigrams, grams, decagrams, kilograms, metric cents, tons etc. Now compare with inches (by the way what's the smaller unit than inch?), feet, yards, miles. Can you tell me quickly how many inches are in 1 mile? Maybe you know it by heart, so let's say in 12 miles. Also Celsius is more logical then Fahrenheit, I already mentioned why. Well the "good" old patriotic system is very impractical and it is intellectual laziness which keeps it still in place. What does it say about us that we are the last in the world?

Posted by
30970 posts

According to Google, of all the countries in the world only three backwaters still use the archaic Imperial system of weights and measures....

  • Liberia
  • Myanmar / Burma
  • U.S.

I grew up with the Imperial system and learned metric when the conversion was done here in the '70s. As I recall, there was no choice in the matter although some people weren't happy with the conversion. Here in B.C. they left the imperial speed signs for a few months and then replaced them all with km/h signs.

I have a general idea of the temperatures regardless of what scale is used. If I need a precise amount, I either use Siri or the metric conversion app on my iPhone. For those that prefer the old fashioned methods, print out a chart such as this one and pack it along....

http://www.rapidtables.com/convert/temperature/celsius-to-fahrenheit.htm

Posted by
17657 posts

Ilja,

Do you carry aroung a balance beam and weights so you can "weigh" things in grams? No.

Do you carry around a scale or tape so you can measure the length of things in cm? Probably not. Some people, mostly geeks do, but most people don't.

Do you carry around a device to tell you the time of day? A watch? Your cell phone? Almost everyone does. It's fair to say that time is our most important measurement.

How many seconds in a minute? 10? No. 100? No. 60!

How many minutes in an hour? 10? No. 100? No. 60!

How many hours in a day? 10? No. 100? No. 24!

So your vaunted decimal system already fails for the most common measurement we make. Come back and argue your point AFTER time has been decimalized.

BTW, how many Newtons does a mass of one Kg weigh? 10? No, 9.8! Why wasn't the meter set so that standard gravitational acceleration is 10 m/sec² or, better yet, 1 m/sec².

I think that the foot is a far more convenient unit of measure than the meter. Note, we have a unit, the yard, which is 91% of the meter, but, except for football, the yard is not commonly used.

Posted by
2353 posts

WOW - I just had to see how you get 40 replies on temp conversion...

Personally I use the 5/9+32

Posted by
4637 posts

Lee, how many days in one week? Seven. How many weeks in one month? Four to five. How many months in one year? Twelve. You got some points. But then how many years in decade? In century? In millennium? But even with seconds, minutes, hours, etc. we are on the same tune as the rest of the world. Well, with little nuance that we have am, pm and they have 24 hour time. But our military, too. Do you know where in the States distances are measured in kilometers? Trails in cross-country skiing. So we are getting there but in snail speed. There are hospitals in the US where they measure patients height in cm and weight in kilograms. And blood pressure in millimeters of mercury, not inches of mercury. That's actually everywhere. Progress seems unstoppable but in this field very slow.

Posted by
17657 posts

I'n not at all against going to a common system, as long as it's not one of the current systems.

We should come up with a better measuring system than the two we are using, and everyone (that means you Europeans and Canadians, too) should start using it. We should decimalize time, then make the unit of distance something that makes sense (eliminates a conversion factor somewhere).

But I said decimalize. We should actually start using a base 8 (Octal) or base 16 (Hexadecimal) numbering system, something that converts readily to a binary, so computers don't have to spend time converting their answers to something that humans can understand.

Why do humans use a base 10 numbering system, anyway? That is the most primitive, archaic aspect of both measuring systems. It's because we have 10 fingers, and we learned to count on our fingers. But dividing something into halves, than quarter, then eights is a much more logical way to do thing because you can bisect a line or an angle directly. Dividing something in tenths is easy with numbers (just move the decimal point), but not so easy with physical objects. (Sometimes it's not so easy to divide a physical object in half, either, but it's easier with liquids.)

Posted by
17657 posts

I always know how much I'm spending for gasoline (in U.S. gallons and
U.S. Dollars) when traveling Europe. It's 2.78 times 1.05 times .615=
cost per mile in U.S. dollars and gallons.

2.78? I think you mean 3.78 liters/gallon.

.615? miles/km is actually .621, but .625 (5/8) works. Multiply by 5, divide by 8. Or just divide by two and add back 1/4 of what you got my dividing by 2.

Posted by
1029 posts

Who would have thought that this would elicit the number of responses that it has? Some a little on the heated side too.

I have come to equate how comfortable it is to temperature as measured in Fahrenheit. This will be true for many Americans. So I need to convert degrees C to F. I could train myself to think in Metric but for temperature it would probably take a year or two. I like Larrys method of C*2 less ten percent etc.

I agree metric generally makes more sense than imperial. But the only way to move to that is probably they way Canada did it. Total immersion.

Posted by
30970 posts

I believe that metric measurements are used by all military forces, including the U.S., for things like artillery targeting, etc. Weapons and ammunition are also expressed using metric units - 9 mm, 5.56 mm, 81 mm, 155 mm, etc. The world seems to be standardized in that respect.

Posted by
12103 posts

I just memorize the temps that are important, those I need to know, from -5C to 100C and their equivalents in F, in order to convert easily from one to the other, basically switching back and forth is no problem Talking to Europeans, I can easily use the system of les français as regards to temperature, distance, volume, ie, ordinary daily life conversions, nothing scientific. When I talk with Americans who know next to nothing or zero on the metric system, I just use the British/American system of inches, miles, temp in F, etc...all the stuff you learned in grammar school. .

When you watch the Vietnam War documentaries, you hear US troops referring to distance in "klics", and meters, not miles or yards.

Posted by
15578 posts

All I want to know is, When renting skis in Europe, if I opt not to use kg, they want to know how many stone I weigh? Stone?? Please give me Kilograms. Anything but Stones.
In my youth, I seem to remember some efforts to switch to the metric system, but it was denounced as a plot of Communist One-Worlders who wanted to sap the vigor of America. They also wanted to teach us to play Soccer, which some called Football, where you actually advanced the ball WITH YOUR FOOT!

Posted by
13967 posts

I just know that 20-30C is comfortable. Over 30 is hot, below 20 and I start thinking about another layer and not wearing sandals. No need to convert.

Posted by
8624 posts

Anything but Stones.

You can't always get what you want......but if you try sometimes well you might find you get what you need.

Posted by
17 posts

Hi Everybody,

I did not mean to open a "can of worms" with my topic on converting Celsius temperatures back to the Fahrenheit scale.

Fortunately, most people have seen but do not know the casino dice table layout and the odds of the dice numbers.

(Note: Playing the "odds" with your "point" on the "line" or "come" is the best casino bet in Las Vegas, Atlantic City, etc.)

I have been told by travelers that of the 7.5 billion people, I am the only person doing the temperature conversions this way.

Posted by
9361 posts

I have no idea what a casino dice table layout even is. When I convert C to F, I just double the C number and add 30.

Posted by
4637 posts

Nancy, you got it! Very simple and sufficient rough estimate. When it's about weather we don't need anything more complicated. If it's about body temperature then I would use the formula. What's the temperature outside? 37 or 38 degrees Celsius. Not a big difference. It's hot. What's your temperature? 37 or 38 degrees Celsius? Quite a difference. Almost normal or a good fever.

Posted by
17657 posts

I think by "casino dice table" he was referring to something similar to the "table" used by Tom_MN early in this thread, where he pairs equivalent temperature from both systems (but with more realistic temperatures). So if the sign says 23°C, you know its about half way between 68°F (20°C) and 77°F (25°C). Pleasant.

BTW does anyone know the one temperature that doesn't have to be converted? It's -40°. It's the same in Celsius and in Fahrenheit, and way too cold, IMO.

Posted by
17 posts

Hi Travelers,

By casino dice table layout, I mean the betting display on the felt. Since seven is in the center of the dice universe, it is also my baseline at 25C = 77F. And in increments of 5 degrees Celsius from baseline in either direction, I see all of the exact Fahrenheit temperatures on the felt faster than calculating a rough, such as Cx2+25 or 30 or %. The 5C increments work out in whole numbers. For units in between the 5C increments, I use the 1.8 factor to get F with a decimal.

This works very well for the everyday-life temperature range of 0-50C which is 32-122F. (freezing to very hot)

Posted by
3320 posts

Back to the original question. With simple mental math skills and a little practice, this will yield a very accurate result: Double the C. temp. Subtract 10% of the result (simply move the decimal one place to the left) from the result, and add 32. I've checked this home made method against a number of phone and computer "unit converters" and have always gotten the same result as the techno machines (which I rarely trust anyway).

Posted by
4468 posts

Celcius was Swedish not French. However, his scale was inverted with 100C being freezing and 0C boiling. It was Carl Linnaeus who turned it around, so really it should be degrees L, but people would get confused with litres ...

Posted by
485 posts

I believe Rick on one of his shows said that he goes by 28 degrees Celsius equals 82 degrees Fahrenheit. I just googled the calculation and came up with 82.4 degrees Fahrenheit. He stated he does not remember anymore than that. Good enough for me.

Ed

Posted by
2429 posts

It's quite easy. Every change of 5 in C is a change of 9 in F. 0 C = 32 F. 5= 41. 10 = 50. ETC

Posted by
607 posts

True story. (I read it somewhere.)

It was in the dog days of August, 1791. Congress was meeting in Philadelphia to draft the American Bill of Rights. James Madison was one of the primary authors of this revered document and had based the US Bill of Rights on the English Bill of Rights of 1689. The delegates from the various states were in a cramp town hall and hotly debating the wording of the proposed Constitution. The delegates could not reach a consensus. The heat and humidity in the hall was stifling. Reports indicated that the temperatures reached 92 degrees Fahrenheit (about 33 degrees Celsius). The heated debate between the delegates only added to the pressure cooker atmosphere. Thomas Jefferson tried to cool things down. He suggested that everybody take off their coats, loosen their neck tabs and roll up their sleeves and get the Constitution done. James Madison was offended. He said that formal legislative decorum should be maintained. He referred to the English Parliament which always maintained pomp and proper attire regardless of the temperature. Jefferson scoffed and stripped down to his undershirt, flexed his biceps and declared that this was not England; this was the United States of America, land of liberty and freedom! Inspired by his gesture, Congress rallied together and finalized the draft of the Constitution, adding in the Second Amendment, the right to bare arms. (I think it was in Mad magazine.)

Posted by
2229 posts

^ ^ You are truly hogging all the fun, funpig! And, I always thought that was about a musket or two over the fireplace...thanks for clearing it up.

Posted by
5436 posts

Ditto to Christi. Had to figure out how this got so many responses. And I use the method that Chris from Basel describes above: °F = (°C ÷ 5 x 9) + 32

Have lived in Europe for nearly 15 years and still think in Fahrenheit. I guess I always will. I kind of have a rough idea of various temperatures, finally.

(EDIT 3/25: Deleted the final section because it was completely wrong!!! Thanks to fellow Okie Jane for the catch)

Posted by
5436 posts

oh you're right Jane! Don't know how I made it 200 in my mind. Have removed that whole illogical bit.