Originally Posted by
Dan Burkhart
No,a 45 degree angle is 100% grade. 100 feet of rise on 100 ft run.
OK then, so it's option (b) 50% means 1rise/2run = atan(0.5) = 26.55 deg.
10% = atan(0.1) = 5.7 deg, and in general for small angles you could apply a rule of thumb that N% ~ N/2 deg. It blows my mind that only a few degrees is such a difficult slope to ride up!