How do you change percent of slope into an angle?

Step 1: Divide the percentage slope by 100.

Step 2: Calculate arctan or tan-1 [=atan() in Excel] of that value to give the angle.

Advanced mathematicians use radians to measure angles, and Excel calculates the angle in radians. However, if you need it in degrees, multiply the last answer by 180/pi. On most calculators you will need to ensure that angles are measured in degrees.

Thus,

if you have a 15% slope, step 1 gives 0.15 and step 2 gives an angle of 0.1489 radians, which is equal to 8.53 degrees (approx).