On the surface this seems like a simple question. With percent gradient being a simple calculation of rise/run *100% (or more precisely tangent of the slope angle *100%). However, how do popular cycling web applications such as mapmyride ridewithGPS and strava determine the maximum gradient of a ride? I recently did a 54 mile ride where the maximum gradient on ridewithGPS was listed as 7.2%. When I actually rode the route the steepest hill had me struggling to turn the pedals in 34-28. A fellow cyclist said the maximum grade of the hill was 16%. Looking back at a route that only includes the 1 mile long hill ridewithGPS lists the maximum grade as 13.2% mapmyride has the steepest section of the hill at 18% and the steepest part of the strava segment for that hill is 16.2%. So how do these websites calculate maximum grade and why does it vary so much between sites and why does the length of the ride change the maximum grade?