Rise/Run to Grade Percent Coversion

I'm trying to figure out how to convert a Rise/Run figure to a grade percent.

EX: 1'-0" rise and 12'-0" run = % grade
I know using a tanget will somehow get the answer I'm looking for, but I don't have a scientific calculator or a forumla for excel to make one.

Any help is appreciated.

 

100 * tan[slope]
y=mx+b
m=slope : rise/run
b=y intercept

so if m=slope then you divide rise/run ..take the tangent of that * 100.

Double check that, but I think that's right.

 

It's been a real long time since trig class, but is tan not a function of an angle rather than of the the quotient of rise over run? I would have thought the answer to the example would have been a much simpler 1 / 12 = .08333~ * 100 = 8.33% grade.