American roof pitch to English degrees

[Russell griffiths]

Morning all

any body know how you convert the yank method of roof pitch to our degrees 

for example. The yanks would say it’s a 4/12 pitch, so it rises 4 inches in 12 inches of run

so would 6/12 mean it rises 6 inches in 12 inches of run so I would think that is 45degrees

 

is there an easy way to work this out, going yank to English, and English to yank

i have 3 roofs all with different pitches so a 15 degree would be what ?????

 

its probably dead simple to work out, but my little brain is so full of other minor crap I thought I would ask. 

Ta very much. 

[ToughButterCup]

Here you are, dad.

 

[PeterW]

(Rise / Run)*45 = degrees pitch

 

or (pitch*12)/45 = rise  for every 12”

 

 

 

 

[Ed Davies]

44 minutes ago, PeterW said:

(Rise / Run)*45 = degrees pitch

 

That happens to work when rise = run. For any other angle it'll be, at best, only an approximation.

 

tan(degrees) = Rise/Run.

 

E.g., for a 6/12 roof that would say 22.5° but it'd actually be atan(6/12) = 26.56…°.

 

>>> for r in range(24): print("%2d/12" % r, degrees(atan2(r, 12)))
...
 0/12 0.0
 1/12 4.763641690726178
 2/12 9.462322208025617
 3/12 14.036243467926479
 4/12 18.43494882292201
 5/12 22.619864948040426
 6/12 26.56505117707799
 7/12 30.256437163529263
 8/12 33.690067525979785
 9/12 36.86989764584402
10/12 39.80557109226519
11/12 42.510447078000844
12/12 45.0
13/12 47.290610042638534
14/12 49.398705354995535
15/12 51.34019174590991
16/12 53.13010235415598
17/12 54.78240703180729
18/12 56.309932474020215
19/12 57.724355685422374
20/12 59.03624346792648
21/12 60.25511870305778
22/12 61.38954033403479
23/12 62.447188423282206

 

So 15° is between 3/12 and 4/12 (actually 3.21539…/12).

[Ed Davies]

1 hour ago, Russell griffiths said:

so would 6/12 mean it rises 6 inches in 12 inches of run so I would think that is 45degrees

 

12/12 would be 45°. 6/12 would be much shallower, 26.56…°.

[ToughButterCup]

That'll teach you to ask @Russell griffiths won't it?   ?

[Temp]

+1 to...

 

Tan(angle) = rise/run

or

Angle = ArcTan(rise/run)

[Russell griffiths]

Cor blimey, my bloody head hurts now. 

 

Thanks all. 

[Ferdinand]

Have a cup of tea, and fit a flat roof instead.