Mickey is 42lbs at 21".

After lots of a research, a Border Collie Rescue board that I am on, we all came up with an average weight scale for each other. I think roughly for every inch you can add or subtract 5lbs:

18" = 30lbs
19" = 35lbs
20" = 40lbs
21" = 45lbs
22" = 50lbs
23" = 55lbs
24" = 60lbs