Great question. I see this question asked frequently on forums. You gauge the decoy spread according to the location, type of hunting scenario, feed, size of the water or field your hunting, capacity to get decoys to X spot, etc. Some smaller pocket water I will run as small of a group as 6 and most are attached to jerk setups, so they are all moving. Big open water setups for divers I will run 12-18 dozen decoys. Sea ducks I typically will run up to 12 dozen decoys. Field hunting for ducks, I run a dozen full bodies up to 30 dozen silhouettes. I used to run up to 15 dozen full bodies with 5-10 dozen shells mixed in. For dark geese we will run 2 dozen to 15 dozen full bodies. This coming weekend we will be targeting cacklers and will more than likely run close to 40 dozen full bodies. For snow geese we have been running 2,500 to 5K rags. Will be cutting that back to about 500 full body snow goose decoys as the birds become more educated. Largest duck spreads I have hunted over were down in the rice field in California where they would leave about 5k floating duck decoys out all season and open holes depending on the blinds we hunted out of. Lots of variables and also dependent on how much work you want to do. I also spend about 85 days a season chasing waterfowl.