Originally Posted by ExMachina
Yup, around 6.6% *average* gradient--that website is wrong.
The website expresses the gradient as a ratio.
In this case it's 1:15.05. If I assume that means one foot of elevation for every 15.05 ft of progress, that works out to (1/15.05)*100 or 6.64%
So it's not an error, just an expression of gradient different than what we are used to.