We use a couple different formulas to give courses a difficulty rating which can be used to rate against other courses.
For Hill Climbs: (H/D*100)*4 + H2/D + D/1000
Whereby: H = difference in height (metres); D = distance in metres
For Circuits: H/D
Whereby: H = elevation gain for whole ride (metres); D = distance in kilometres
(please note this difficulty rating is not an overall rating but a difficulty factor for every kilometre which is based on the average amount of vertical metres climbed every kilometre)