What size hole should be used for a birdhouse?

The size of the hole for a birdhouse should be specific to the type of bird you want to attract. Generally, a hole size of 1-1.5 inches is suitable for small birds like chickadees and wrens, while larger birds like bluebirds may require a hole size of 1.5-2 inches. It is important to research the specific bird species you want to attract to determine the appropriate hole size for their needs.