How can you directly convert fahrenheit to celsius if they were created with different methods of measurement?
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It’s the same method of measurement, just on a different scale. As they are both straight lines you can use a maths formula to convert one to another.
Fahrenheit minus 32, then take 5/9ths of that = Celsius
Celsius: times by 1.8, add 32
I’m not sure I understand your question when you say “methods of measurement” But as long as the metric you are measuring is the “same thing” you can convert from whatever units you use to other units and just about everything can be measured using different “methods”
For example when measuring the weight of something you can either use a balance scale. Those are ones where you put a weight on each side and when it “balances” each side has the same weight. So the way you measure weight using that a known weight on one side, an unknown weight on the other side.
Or you can use a spring scale if you have a bathroom scale that is what you are using, where you stand on a plate and then how much the spring compresses tells you the weight.
Both of those are entirely different “methods of measurement” that give you a weight, and that weight can be in whatever units you want.
I understand what you are trying to ask. The Fahrenheit and Celsius scales were developed independently. Normally when that happens you don’t get clean conversion ratios like 9/5. See the conversion ratios for length and masss to see what I mean.
It looks like the standard for the Fahrenheit scale was modified in the 1770s to fix the freezing point of water to 32 and the boiling point of water to 212. This was done because of the popularity how the Celsius scale worked. The previous Fahrenheit standard used a brine solution and body temperature. The Celsius *method* proved easier for calibration.
So, the Fahrenheit standard simply pegged its scale to 180C/100 + 32 very early.
They both measure the same thing using different units. Like centimetres and inches. It’s easy to find a formula thatnworks to convert one value into the other. Joules and calories, shoe sizes based upon a new born’s foot length (smaller in the US than in Europe)
Two important details:
Firstly, they both measure the same thing: temperature. And for every possible temperature a thing can be, Fahrenheit has a number for it, and so does Celsius. It doesn’t matter what numbers each system actually calls it; the only important part is that both systems have a number for every possible temperature. The fancy math jargon for this would be that the two scales have the same *domain*.
The other important point is that there are no weird jumps or skips in either scale. Fahrenheit doesn’t, like, go up to 50 degrees, then suddenly skip 51 through 99, and go straight to 100. It always goes up smoothly, and so does Celsius. It might feel stupid to bring that detail up, but believe me, it’s important. The fancy math jargon for this is called *continuity*.
As long as you have these two things — two scales having the same domain, and both of them being continuous — then it is *guaranteed* by math that there will be a way to convert one to the other, and you can find a formula for it. It doesn’t matter how either scale was created or how either of them work.
Both scales are linear so an increase of a certain amount of energy will always result in the same amount of temperature change, regardless of the starting temperature.
As a result it’s a simple case of looking at the range over which water is liquid in the Fahrenheit scale (180: 32 – 212) and dividing by 100 from the Celsius scale to see that a change of 1°C is always the same as a change of 1.8°F. Then factor in that 0°C is the same as 32°F to get the formula:-
F = 1.8C + 32
All you need to know to convert them is the following two things:
(A) An assumption that both use a linear scale. (that the 1 degree difference between, say, 2 degrees and 3 degrees is the same size difference as the 1 degree difference between 50 and 51 degrees, or 90 and 91 degrees, etc. That one degree of difference means the same thing at all places along the scale, for both scales.)
(B) You also need two sample temperatures that you know are the same phenomenon for both scales so you know they equate. That can fix the two scales relative to each other. For this you can use water’s freezing and boiling points.
Whatever Fahrenheit claims is water’s boiling point in its scale is the same physical temperature as what Celsius claims water’s boiling point is.
Whatever Fahrenheit claims is water’s freezing point in its scale is the same physical temperature as what Celsius claims water’s freezing point is.
That tells you that what Fahrenheit claims should be called 32 is the same physical thing as what Celsius claims should be called 0. And what Fahrenheit claims should be called 212 is the same physical thing as what Celsius claims should be called 100.
That is how the conversion formula is made.
The span between freezing and boiling takes Fahrenheit takes 180 degrees to cover, while Celsius covers that same range in 100 degrees.
That tells you that one Celsius degree is 1.8 times as “big” as one Fahrenheit degree. And you know the zero point of Celsius is the place where Fahrenheit is 32.
Putting those two together gives you:
F = 1.8 C + 32
(Or, the other way:)
C = (F – 32) / 1.8
(For either of the above, some places show the 1.8 part of the formula as 9/5. It’s the same thing.)
They are both linear scales, so with some multiplication and addition you can map one onto the other.
Just like with Inches and Centimeters. Pounds and Newtons. Liters and Gallons. They all can be mapped to each other with just a little math.
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