The most popular size for door hangers tends to be 3.5 inches by 8.5 inches. This size is large enough to be noticeable and provide sufficient space for an effective message or design, but not so large as to be cumbersome or intrusive.

Some prefer a slightly larger size, like 4.25 inches by 11 inches, for added visibility and space for more detailed information or more elaborate designs. The choice between these sizes often depends on the specific marketing goals, the amount of information to be included, and the budget for the campaign.