Calculating % Grade of a Hill

[uforgot]

ah, come on. Walk 10 feet... now if when you get to the end of the 10 feet you are 2 feet higher than you were in the beginning, that's a 20% grade.

Careful! It's not quite as easy as that. If you walk up 10 feet and have risen 2 feet, your horizontal displacement is not 10, it's 9.8, which makes it 20.4%. Not an issue for a small rise, but it certainly is if the rise gets larger! If you walk up a 10 feet slope and rise 5, (30 degrees) it's not 50%, but 57%!

Remember when your Geometry teacher taught you the Pythagorean Theorem and you wondered..."when am I EVER going to use this?" Well, here ya go.