4/12 pitch

Easy way to figure pitch angles is start with a 12/12 or 45º then a 6/12=22.5º then a 3/12=11.25º then divide 3 into 11.25=3.75 as there's 3" from 3/12 to 6/12 so each inch of rise is equal to 3.75º then we get:

12/12=45º
11/12=41.25º
10/12=37.5º
9/12=33.75º
8/12=30º
7/12=26.25º
6/12=22.5º
5/12=18.75º
4/12=15º
3/12=11.25º
2/12=7.5º
1/12=3.75º

T_Bone

Jerry has it right. Your way is an approximation that isn't too bad when you're close to zero or 45 degrees, but it's way off when you get towards the middle (22.5 degrees).

12/12=45º (correct)
11/12=41.25º (actually 42.5)
10/12=37.5º (actually 39.8)
9/12=33.75º (actually 36.9)
8/12=30º (actually 33.7)
7/12=26.25º (actually 30.3)
6/12=22.5º (actually 26.6)
5/12=18.75º (actually 22.6)
4/12=15º (actually 18.4)
3/12=11.25º (actually 14.0)
2/12=7.5º (actually 9.5)
1/12=3.75º (actually 4.8)

That 3.4 degree error would be enough to spoil Kevin's project.

And if you try to use your method to figure out angles greater than 45 degrees, it really goes south, since the tangent of 90 degrees is infinity.

Your absolutly correct.

As soon as I opened the thread this morning I knew I was wrong as you can't have equal vertical spaces and rise a equal number of degrees.

Thanks for catching my mistake!

T_Bone

So wouldn't that be the arcsine(4/12) = 19.5 degrees?