# How °F = 9/5(°C) + 32

1. Dec 18, 2016

### parshyaa

How we got this formula i know that the ratio of scale difference is 180/100 =9/5 but why to add 32, is it because °F at 0°c is + 32

2. Dec 18, 2016

### Vanadium 50

Staff Emeritus
Yes. Plug in a few numbers and you'll see.

3. Dec 19, 2016

### Battlemage!

The 0 was moved to be the freezing point of water. Here is some info:

http://www.todayifoundout.com/index.php/2014/12/fahrenheit-scale-isnt-arbitrary-seems/

(interestingly, originally the freezing point of water was 100°C, and the boiling point was 0°C, but Carl Linnaeus made that modification- Good read)

4. Dec 19, 2016

### FactChecker

I'm not sure how clear it is in the references, but for seafaring nations like Britain and Denmark, the freezing temperature of salt water is very significant. So setting the 0 of the Fahrenheit scale at that point makes sense. Maritime issues drove the development of clocks, thermometers, etc.

5. Dec 20, 2016

### parshyaa

6. Dec 23, 2016

### James Pelezo

7. Dec 23, 2016

### David J Wilson

The other well-known conversion method, based on the -40° coincidence of the two scales is, I think, easier to remember. The fact that I no longer remember it is utterly irrelevant.

8. Dec 24, 2016

### Battlemage!

Ha that is a cool way to see it.

9. Dec 24, 2016

### David J Wilson

I fortified myself to argue with you with the aid of Google, which asserts that seawater freezes at 28.4°F. I seem to remember that Fahrenheit produced the lowest temperature possible to him in the day in his laboratory to get to his zero.

10. Dec 24, 2016

### FactChecker

I am certainly not an expert in the history of this. I have seen it said a few times that 0°F is the freezing point of brine. (This reference says that 0°F was the lowest temperature he could get reliably by freezing brine. https://en.wikipedia.org/wiki/Brine . That makes sense to me.) I might have seen it explained as important for sailing, I don't remember. Maybe I just erroneously jumped to that conclusion. Certainly he would have wanted to include the temperature of freezing sea water in his temperature range.

Last edited: Dec 24, 2016
11. Jan 1, 2017

### rbelli1

Is there an explanation as to why the two scales match up so nicely? The defined points are rather arbitrarily chosen.

BoB

12. Jan 4, 2017

### glappkaeft

It is because the original definition of Fahrenheit was replaced in 1776 with one where 32 °F is 0 °C and 212 °F is 100 °C.

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