Why is it so simple to convert between °F and °C?

[Jaskalas]

Yes, but it's -160 Bears. And that sounds a lot colder than -40, so I propose we switch to my new units of temperature measurement.

-160 bears... that's a lot of missing body heat. Imagine dropping that on a city. Flash freeze.

 

[Schmide]

F->C
(F-32)/(9/5)

C->F
(C*(9/5))+32

The mental way using decimal shift.

F->C

(F-32) / 2 + 11%

C->F

(C - 10%) * 2 + 32

Examples

70F in C

70-32 = 38 /2 = 19 + 11% (1.9+0.19=2.09) = 21.09 (actual 21.1)

21C in F

21 - 10% (2.1) = 18.9 * 2 = 37.8 + 32 = 69.8

 

[DrPizza]

Great comments and insight.

I know they are the same thing and both are linear... but why is it a simple 1.8 ratio?
Why not 1.8135?

It's 1.8 because
water freezing 32F, water boiling 212F Difference = 180
water freezing 0C, water boiling 100C Difference = 100

180/100 = 1.8

If water boiled at 213F (but that's still where they set it for the C scale), then the ratio would be 1.81 (181/100)


worth noting: I'm not sure what it is without googling, but as the years passed since those two scales were developed, measurements were able to get more and more precise. Tiny changes affect the boiling point in tiny ways. I doubt that the boiling point of water at 1 atmosphere of pressure is *exactly* 212.000000000000000F. At some point, once such precision was reached, one system or the other system had to be standardized. And then, the other system's standards would be based on that as well. I presume that the standard is for the Celsius scale.

 

[Fayd]

Both scales are linear (the graduations are evenly spaced.) Thus, I can arbitrarily determine my own scale for a thermometer:

0 degrees bear is the temperature of bear shit I found in the woods on a Saturday in late November. 100 degrees bear is what I mark the rectal temperature of the bear on my thermometer. That is, pop that thermometer out, draw a line where the mercury (or dyed alcohol) is, and call that line 100.

On your Fahrenheit scale, my 0 is your 40 degrees. My 100 degrees is your 90 degrees. So, my scale goes up 100 degrees, while your scale only goes up 50 degrees. That is, a change of 2 degrees on my scale corresponds to a change of 1 degree on your scale. Now, to do a conversion, we merely have to do a slight shift.

Let's say that you measure something to be 50 degrees F. You want to convert it to Bears. You note that it's 10 degrees above the F temperature that corresponds to the 0 on my scale. [In other words, 50 - 40 = 10]. And, you know that 1 of your degrees F is equal to 2 of my degrees B. So, 10*2 = 20.

The formula, thus, looks like this:
B=2(F-40)

Or, to convert the other way, let's say I measure a temperature of 60 degrees Bear. I'd know that each of my degrees was 2 of your degrees. So, I'm 30 of your degrees above my zero. My zero is 40 of your degrees. That makes it 70 of your degrees.
F= (1/2)B + 40


0C corresponds to 32F
100C corresponds to 212F
So a change of 100 degrees C = a change of 180 degrees F
100/180 = 5/9
180/100 = 9/5
And, I think you can figure out why you add or subtract the 32 now.

i second bear for the official temperature of atot.

 

[Imp]

You bastards keep your A/C at 70 F, which is like 20 C. Thanks for helping me remember...

 

[randay]

Both scales are linear (the graduations are evenly spaced.) Thus, I can arbitrarily determine my own scale for a thermometer:

0 degrees bear is the temperature of bear shit I found in the woods on a Saturday in late November. 100 degrees bear is what I mark the rectal temperature of the bear on my thermometer. That is, pop that thermometer out, draw a line where the mercury (or dyed alcohol) is, and call that line 100.

On your Fahrenheit scale, my 0 is your 40 degrees. My 100 degrees is your 90 degrees. So, my scale goes up 100 degrees, while your scale only goes up 50 degrees. That is, a change of 2 degrees on my scale corresponds to a change of 1 degree on your scale. Now, to do a conversion, we merely have to do a slight shift.

Let's say that you measure something to be 50 degrees F. You want to convert it to Bears. You note that it's 10 degrees above the F temperature that corresponds to the 0 on my scale. [In other words, 50 - 40 = 10]. And, you know that 1 of your degrees F is equal to 2 of my degrees B. So, 10*2 = 20.

The formula, thus, looks like this:
B=2(F-40)

Or, to convert the other way, let's say I measure a temperature of 60 degrees Bear. I'd know that each of my degrees was 2 of your degrees. So, I'm 30 of your degrees above my zero. My zero is 40 of your degrees. That makes it 70 of your degrees.
F= (1/2)B + 40


0C corresponds to 32F
100C corresponds to 212F
So a change of 100 degrees C = a change of 180 degrees F
100/180 = 5/9
180/100 = 9/5
And, I think you can figure out why you add or subtract the 32 now.

did you find the bear shit in the woods? or was it somewhere non-wooded.

how many bears is the sun?

 

[The Boston Dangler]

it's 87F outside right now. is that 348 bears?

i propose we make atmospheric pressure at sea level 1 polarBear, or 1 pB

 

[OverVolt]

Both scales are linear (the graduations are evenly spaced.) Thus, I can arbitrarily determine my own scale for a thermometer:

0 degrees bear is the temperature of bear shit I found in the woods on a Saturday in late November. 100 degrees bear is what I mark the rectal temperature of the bear on my thermometer. That is, pop that thermometer out, draw a line where the mercury (or dyed alcohol) is, and call that line 100.

On your Fahrenheit scale, my 0 is your 40 degrees. My 100 degrees is your 90 degrees. So, my scale goes up 100 degrees, while your scale only goes up 50 degrees. That is, a change of 2 degrees on my scale corresponds to a change of 1 degree on your scale. Now, to do a conversion, we merely have to do a slight shift.

Let's say that you measure something to be 50 degrees F. You want to convert it to Bears. You note that it's 10 degrees above the F temperature that corresponds to the 0 on my scale. [In other words, 50 - 40 = 10]. And, you know that 1 of your degrees F is equal to 2 of my degrees B. So, 10*2 = 20.

The formula, thus, looks like this:
B=2(F-40)

Or, to convert the other way, let's say I measure a temperature of 60 degrees Bear. I'd know that each of my degrees was 2 of your degrees. So, I'm 30 of your degrees above my zero. My zero is 40 of your degrees. That makes it 70 of your degrees.
F= (1/2)B + 40


0C corresponds to 32F
100C corresponds to 212F
So a change of 100 degrees C = a change of 180 degrees F
100/180 = 5/9
180/100 = 9/5
And, I think you can figure out why you add or subtract the 32 now.

You're good at what you do.

 

[acheron]

And that's how centigrade was developed. Fahrenheit I think was just drunk.

0F is the freezing point of salt water, more or less. I had thought 100 was intended to be body temperature, but I just looked it up on Wikipedia and it looks like 96 was intended to be body temperature (and later adjustments to the scale pushed it up to 98ish), and 100 wasn't supposed to be anything in particular. https://en.wikipedia.org/wiki/Fahrenheit#History

 

[acheron]

As far as the OP question: Fahrenheit is designed so freezing and boiling water are 180 degrees apart. Celsius is designed so they are 100 apart. That's where the number comes from.

 

[rudeguy]

I just do it in my head.

If I'm working with 300C temp, that's 3x boiling, so 636F
Or the opposite, if I'm working with 450F, that's a little more than 2x boiling, so a little over 200C

As for the weather temp, who cares?

 

[Red Squirrel]

I usually just use google. (ex: "30C in F" and it will tell you the conversion) Though if America got with the times and use metric like everybody else there would be no need to convert as often.

 

[edro]

Ah... so the 180° was probably so it could be related to a circle... being 1/2 of 360°.

This is totally making sense now.

 

[edro]

Fahrenheit proposed his temperature scale in 1724, basing it on three reference points of temperature.[7] In his initial scale (which is not the final Fahrenheit scale), the zero point is determined by placing the thermometer in brine: he used a mixture of ice, water, and ammonium chloride, a salt, at a 1:1:1 ratio. This is a frigorific mixture which stabilizes its temperature automatically: that stable temperature was defined as 0 °F (−17.78 °C). The second point, at 32 degrees, was a mixture of ice and water without the ammonium chloride at a 1:1 ratio. The third point, 96 degrees, was approximately the human body temperature, then called "blood-heat".[10]
According to a letter Fahrenheit wrote to his friend Herman Boerhaave,[11] his scale was built on the work of Ole Rømer, whom he had met earlier. In Rømer's scale, brine freezes at zero, water freezes and melts at 7.5 degrees, body temperature is 22.5, and water boils at 60 degrees. Fahrenheit multiplied each value by four in order to eliminate fractions and increase the granularity of the scale. He then re-calibrated his scale using the melting point of ice and normal human body temperature (which were at 30 and 90 degrees); he adjusted the scale so that the melting point of ice would be 32 degrees and body temperature 96 degrees, so that 64 intervals would separate the two, allowing him to mark degree lines on his instruments by simply bisecting the interval six times (since 64 is 2 to the sixth power).[10][12]
Fahrenheit observed that water boils at about 212 degrees using this scale. Later, other scientists[who?] decided to redefine the scale slightly to make the freezing point exactly 32 °F, and the boiling point exactly 212 °F or 180 degrees higher.[citation needed] It is for this reason that normal human body temperature is approximately 98° (oral temperature) on the revised scale (whereas it was 90° on Fahrenheit's multiplication of Rømer, and 96° on his original scale).[13]

Interdasting.

 

[Slammy1]

(212-32)=180 (Diff between freezing and boiling F)
100-0 = 100

180/100=1.8... It's exact, but I think they adjusted the F scale so freezing is exactly 32 and boiling is exactly 212.

 

[Paul98]

Ah... so the 180° was probably so it could be related to a circle... being 1/2 of 360°.

This is totally making sense now.

No, there were two linear scales made. One where freezing point of water and boiling point of water were 0 and 100, where you can still go linear up and down from that. For the other you have different points, like body temp, and freezing point of water salt solution approximation. Both are linear scales.

For each 1 degree of change in F, you get 5/9 degree of change in C.

Given the above statement, if both had same 0 point aka lets say both 0C and 0F was freezing point of water. If you had something at 100F, what would the temperature be in C?

 

[Paperdoc]

edro's post of 09/12 is pretty close to what I was taught years ago, but more detailed. the Fahrenheit scale was developed AFTER the Celsius scale to "improve" on two concerns.

(a) lots of real temperatures (especially in labs) were lower than 0C, and negative numbers were not popular. So setting the freezing point of water at some higher positive number provided a solution at that time.

(b) The use of decimals for values between integers was not well accepted either, but careful observations made it clear that some temperatures were more like 27½C, and not just whole numbers. Thus came the decision to split the range between the freezing point and boiling point of water into 180 degrees (new Fahrenheit ones) rather than 100, nearly doubling the resolution or granularity of the system.

As many have said, both systems are defined as linear scales with the SAME reference points. Thus the conversion formulae are EXACT, not just approximations.

 

[DrPizza]

edro's post of 09/12 is pretty close to what I was taught years ago, but more detailed. the Fahrenheit scale was developed AFTER the Celsius scale to "improve" on two concerns.

(a) lots of real temperatures (especially in labs) were lower than 0C, and negative numbers were not popular. So setting the freezing point of water at some higher positive number provided a solution at that time.

(b) The use of decimals for values between integers was not well accepted either, but careful observations made it clear that some temperatures were more like 27½C, and not just whole numbers. Thus came the decision to split the range between the freezing point and boiling point of water into 180 degrees (new Fahrenheit ones) rather than 100, nearly doubling the resolution or granularity of the system.

As many have said, both systems are defined as linear scales with the SAME reference points. Thus the conversion formulae are EXACT, not just approximations.

I used to think they were exact, but when I typed my response above about standards, I ended up looking to see what the standards actually are. The Celsius scale standard is the critical point of water at 0.01C. After digging for a while, the difference between freezing and boiling is not exactly 100C, it's actually 99.975 C. So, the 180/100 is simply, "darn good enough" but not exact.

 

[Fenixgoon]

even easier:

1 ksi-in^1/2 ~~ 1.1 MPa-m^1/2

 

[Rakehellion]

Both scales are linear (the graduations are evenly spaced.) Thus, I can arbitrarily determine my own scale for a thermometer:

0 degrees bear is the temperature of bear shit I found in the woods on a Saturday in late November. 100 degrees bear is what I mark the rectal temperature of the bear on my thermometer. That is, pop that thermometer out, draw a line where the mercury (or dyed alcohol) is, and call that line 100.

On your Fahrenheit scale, my 0 is your 40 degrees. My 100 degrees is your 90 degrees. So, my scale goes up 100 degrees, while your scale only goes up 50 degrees. That is, a change of 2 degrees on my scale corresponds to a change of 1 degree on your scale. Now, to do a conversion, we merely have to do a slight shift.

Let's say that you measure something to be 50 degrees F. You want to convert it to Bears. You note that it's 10 degrees above the F temperature that corresponds to the 0 on my scale. [In other words, 50 - 40 = 10]. And, you know that 1 of your degrees F is equal to 2 of my degrees B. So, 10*2 = 20.

The formula, thus, looks like this:
B=2(F-40)

Or, to convert the other way, let's say I measure a temperature of 60 degrees Bear. I'd know that each of my degrees was 2 of your degrees. So, I'm 30 of your degrees above my zero. My zero is 40 of your degrees. That makes it 70 of your degrees.
F= (1/2)B + 40


0C corresponds to 32F
100C corresponds to 212F
So a change of 100 degrees C = a change of 180 degrees F
100/180 = 5/9
180/100 = 9/5
And, I think you can figure out why you add or subtract the 32 now.

Whoah there, Mr. Science. I think he's asking why you multiply by 1.8 and not 1.80271 or something.

 

[Rakehellion]

This. There's no magic, someone smart just said "Well, There's two points, the boiling point of water and the freezing point of water, and I think that should be divided into 100. Yeah, that works."

And that's how centigrade was developed. Fahrenheit I think was just drunk.

Centigrade is just as arbitrary as Fahrenheit. There's nothing so special about water that we needed another system to learn.

 

[DrPizza]

Centigrade is just as arbitrary as Fahrenheit. There's nothing so special about water that we needed another system to learn.

http://forums.anandtech.com/showpost.php?p=35485380&postcount=42

 

[uclaLabrat]

Centigrade is just as arbitrary as Fahrenheit. There's nothing so special about water that we needed another system to learn.

So weird, 5 minutes of reading could have shown you that there is nothing arbitrary about either system, but nope...just plowed right into the idiocy.

Well done.

 

[Leros]

I hope DrPizza never gives put on a standards board.

 

[Howard]

even easier:

1 ksi-in^1/2 ~~ 1.1 MPa-m^1/2

What the hell?