If you don't have a GPS or altimeter, you can find the beginning and ending elevation of your route on Googlearth and if you know the distance covered, input the info into this website

http://www.csgnetwork.com/inclinedeclinegradecalc.html

and it will calculate the grade for you.

I have no luck with routeslip or bikely etc. Not sure if it's because I'm on a Mac or Canadian or both....