That's the scale I've usually seen people go by. Although sometimes for longer rides it's hard to go by the whole averages. I mean I leave my house and do ~10 rolling miles to meet a group, then we ride along the coast for a while, go over some mountain passes, ride back along the coast and then I take a flattish route home... so the whole thing may be 5,000 feet in 80 miles but I'd say it's more than rolling because it's all at once... On the other hand I did 4,000 feet in 37 miles in the foothills yesterday but never had a single climb that was more than 500 feet and the whole thing topped out at 1,000 so I'd hardly call it mountainous. IMO they are both "hilly" rides.