Grade percent and grade degree are not the same. A 100 percent (%) grade is equal to a 45 degree (°) grade.
Be careful not to overestimate the grade percent otherwise the vehicle may not be geared for it maximum potential speed or a motor that is too large may be used causing the project will cost more than necessary.
Also, be careful not to underestimate the grade percent otherwise the vehicle may not make it up the grades that it needs to or the motor and controller may overheat due to not being powerful enough.
Keep in mind as a point of reference that the steepest public road in the United States is a 70 percent grade.