There are 27 states that have some form of citizen initaitve or referendum process. Eleven of these states require some sort of size for signature petitions. Eight of these states have a petition size requirement that would allow 8.5×11 sized petition.
Washington state's required size is the largest in the country.
The state of Oregon also allows petitions circulated on county issues to be 8.5×11. The two largest cities in Washignton, Seattle and Spokane, allow 8.5×11 petitions.