Celcius to Farenheit conversion - where does the 5/9 come from

euser1984

Hi,
Im learing computer programming as this conversion is the first I've run into. I know that -32 is used but how does the 5 divided by 9 work.

Thanks.

Unregistered.

euser1984 wrote: »

Hi,
Im learing computer programming as this conversion is the first I've run into. I know that -32 is used but how does the 5 divided by 9 work.

Thanks.

It's (temp - 32) * (5/9) to get from F to C.

Michael Collins

euser1984 wrote: »

Hi,
Im learing computer programming as this conversion is the first I've run into. I know that -32 is used but how does the 5 divided by 9 work.

Thanks.

Yes 32 °F is the offset, as you're aware, but there's also a scailing difference between the two.

For example:
Freezing point in degrees Celsius is 0°
Freezing point in degrees Fahrenheit is 32°

Boiling point in degrees Celsius is 100°
Boiling point in degrees Fahrenheit is 212°

So now we take the offset of 32 away from the Fahrenheit figures, we'll call this the "FahCel" scale for now! Sort of half-way between the two scales:

Freezing point in degrees Celsius is 0°
Freezing point in degrees FahCel is 0°

Boiling point in degrees Celsius is 100°
Boiling point in degrees FahCel is 180°

Clearly, even though we have corrected for the offset (i.e. 0° Celsius corresponds to 0° FahCel), there's still a scailing difference because the boiling points are not equal. In other words, 1 degree Celsius ≠ 1 degree Fahrenheit.

To see what we must multiply to fix this we write:

[latex] \displaystyle 180^\circ \hbox{ FahCel} \times \hbox{scale} = 100^\circ \hbox{ Celsius}[/latex]

[latex] \displaystyle \hbox{scale}= \frac{100^\circ \hbox{ Celsius}}{180°^\circ \hbox{ FahCel}} = \frac{5}{9} [/latex]

Which means 1 degree Fahrenheit is equal to 5/9 degrees Celsius.

So to convert from degrees Fahrenheit to degrees Celsius we subtract 32 and multiply by 5/9:

[latex] \displaystyle C = \frac{5}{9}(F-32) [/latex]

euser1984

Michael Collins wrote: »

euser1984 wrote: »

Hi,
Im learing computer programming as this conversion is the first I've run into. I know that -32 is used but how does the 5 divided by 9 work.

Thanks.

Yes 32 °F is the offset, as you're aware, but there's also a scailing difference between the two.

For example:
Freezing point in degrees Celsius is 0°
Freezing point in degrees Fahrenheit is 32°

Boiling point in degrees Celsius is 100°
Boiling point in degrees Fahrenheit is 212°

So now we take the offset of 32 away from the Fahrenheit figures, we'll call this the "FahCel" scale for now! Sort of half-way between the two scales:

Freezing point in degrees Celsius is 0°
Freezing point in degrees FahCel is 0°

Boiling point in degrees Celsius is 100°
Boiling point in degrees FahCel is 180°

Clearly, even though we have corrected for the offset (i.e. 0° Celsius corresponds to 0° FahCel), there's still a scailing difference because the boiling points are not equal. In other words, 1 degree Celsius ≠ 1 degree Fahrenheit.

To see what we must multiply to fix this we write:

[latex] \displaystyle 180^\circ \hbox{ FahCel} \times \hbox{scale} = 100^\circ \hbox{ Celsius}[/latex]

[latex] \displaystyle \hbox{scale}= \frac{100^\circ \hbox{ Celsius}}{180°^\circ \hbox{ FahCel}} = \frac{5}{9} [/latex]

Which means 1 degree Celsius is equal to 5/9 degrees Fahrenheit.

So to convert from degrees Fahrenheit to degrees Celsius we subtract 32 and multiply by 5/9:

[latex] \displaystyle C = \frac{5}{9}(F-32) [/latex]

Thanks for that. I keep thinking 5/9 is a fraction.

LeixlipRed

It is a fraction.

28064212

euser1984 wrote: »

Thanks for that. I keep thinking 5/9 is a fraction.

euser1984

euser1984 wrote: »

Michael Collins wrote: »

euser1984 wrote: »

Hi,
Im learing computer programming as this conversion is the first I've run into. I know that -32 is used but how does the 5 divided by 9 work.

Thanks.

Yes 32 °F is the offset, as you're aware, but there's also a scailing difference between the two.

For example:
Freezing point in degrees Celsius is 0°
Freezing point in degrees Fahrenheit is 32°

Boiling point in degrees Celsius is 100°
Boiling point in degrees Fahrenheit is 212°

So now we take the offset of 32 away from the Fahrenheit figures, we'll call this the "FahCel" scale for now! Sort of half-way between the two scales:

Freezing point in degrees Celsius is 0°
Freezing point in degrees FahCel is 0°

Boiling point in degrees Celsius is 100°
Boiling point in degrees FahCel is 180°

Clearly, even though we have corrected for the offset (i.e. 0° Celsius corresponds to 0° FahCel), there's still a scailing difference because the boiling points are not equal. In other words, 1 degree Celsius ≠ 1 degree Fahrenheit.

To see what we must multiply to fix this we write:

[latex] \displaystyle 180^\circ \hbox{ FahCel} \times \hbox{scale} = 100^\circ \hbox{ Celsius}[/latex]

[latex] \displaystyle \hbox{scale}= \frac{100^\circ \hbox{ Celsius}}{180°^\circ \hbox{ FahCel}} = \frac{5}{9} [/latex]

Which means 1 degree Celsius is equal to 5/9 degrees Fahrenheit.

So to convert from degrees Fahrenheit to degrees Celsius we subtract 32 and multiply by 5/9:

[latex] \displaystyle C = \frac{5}{9}(F-32) [/latex]

Thanks for that. I keep thinking 5/9 is a fraction.

Sorry. I just saw it expressed differently.

Unregistered.

Michael Collins wrote: »

Which means 1 degree Celsius is equal to 5/9 degrees Fahrenheit.

Surely it's the other way around.

1F = 5/9C ?

Delphi91

Unregistered. wrote: »

Surely it's the other way around.

1F = 5/9C ?

100 C = 180 F

Therefore 1 C = (180/100)F
i.e. 1 C = (9/5) F

or 1F = 5/9C

Unregistered.

Delphi91 wrote: »

1F = 5/9C

Well done.