Not neccessarily a 50+ topic, but I could use some help.

Trying to calculate the grade of a hill I go up.

According to Gmaps pedometer, the hill is .7809 mile, and elevation is 731 feet. Converted the miles to feet and came up with 4123 feet, and calculated a 17% grade. Could this be right? I knew it was a steep hill, but, egad....