Converting Rise/Run to Degrees?

[Mike P. Wagner]

I is there a quick rule for converting rise/run (the way an angle is specified for rafters 5" per foot) to degrees? I think mathematically its the arctan. But I have to believe that carpenters have been doing the conversion for years w/o a calculator.

I'm cutting come rafter plates on my bt3100.

Thanks,

Mike

[LCHIEN]

Arctan(rise/run) = degrees
rise and run must be the same units
so if rise in inches and run in feet

then Arctan(rise/(12 x run)) = degrees.
make sure calculator is in degrees mode, not radians or other angle modes.

[LarryG]

quote:Originally posted by Mike P. Wagner

But I have to believe that carpenters have been doing the conversion for years w/o a calculator.

Sure, they do it "visually," using a framing square, or a speed square.