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# Converting Fahrenheit to Celsius

Converting Fahrenheit to Celsius. Created by Sal Khan and Monterey Institute for Technology and Education.

## Want to join the conversation?

• it is difficult the understand the formula of celsius and farenheit
• Just break the formula down in steps. Eg Farenheit to Celcius:

Take Temp in Celcius, 1. divide by 5 (easy math), 2. then multiply by 9, 3. then add 32.
So for 30 Celcius,
step 1. 30/5 = 6.
step 2. 6*9 = 54
step 3. 54 + 32 = 86 F

For the farenheit to Celcius, just reverse the order and do the opposite function in each steps:
1. _subtract 32
2. divide by 9
3. multiply by 5
Eg. So for 100 F =
step 1 (subtract 32) 100 - 32 = 68
step 2.(divide by 9) 68/9 = 7.56
step 3. (mult by 5) 7.56*5 = 37.8 C

Good rule of thumb is that Celcius is USUALLY a SMALLER number than Fahrenhet (until you are LESS than -40 F), that's a quick way to check to see if you did it right.
• How do you calculate Farenheit to Kelvin?
• You don’t. Convert to Celsius then to kelvin
• how is F and C equal at -40
• Since they are both scales measuring the same thing and are somewhat proportional, they are bound to meet or cross at some point.

If F = 9/5 C + 32,
then at C = - 40, then 9/5 (-40) + 32 = -72 + 32 = -40 F

Looking at the equation, we see that this point must meet 2 criteria
- be below 0 ˚C
Since the freezing point of water is higher than in the F scale than the C scale (32 ˚F vs. 0 ˚C) and both scales "grow" apart even further from there, the point of the scales crossing or intersecting would have to be below 0 ˚C, and below by more than 32˚ to bring the F scale down into negative territory as well

- a multiple of "5" on the C scale
So that the equation would give a whole number

For this particular equation, there is only 1 number that satisfies these conditions and fits the equation and that is -40.
• in the why is one? 10-9=9 not 1
• 9 and 10 are only one digit apart, so the answer is 1.
(1 vote)
• Why are there still several units for basic things like distance, weight and temperature?
Pros and cons?
The only positive thing about using different systems is that you can adjust the scale for a certain purpose, let's take kelvin for instance. Temperature is a measurement of atom's movement, so basing a temperature scale on that specific property seems like a handy thing when working with chemistry.
But in everyday life to me it seems like a better thing to share one standard system =)

Any thoughts?
• I really agree with you on this. I feel like having a system that will make complete logical sense and be easy to remember/figure out would be so much better. Why is the US always the "wierd" one with things like this. I feel like the metric system and celsius would make things so much easier than having to do feet, and inches, and miles, and Farenheit.... just my opinion...
• why are temperatures greater for the fahrenheit scale than the celsius scale above 40 but lesser below 40?
• Is there a video on thermocouples? Because I can't seem to find any.
• Here is another great formula:

Fahrenheit to Celsius: F - 32 X 5 divided by 9

Celsius to Fahrenheit: C X by 9, then divide by 5, then add 32