Measurements to Build a Birdhouse
The size you will build a birdhouse obviously depends on the size of the bird.
Large birds prefer a house with space to stretch their wings. Smaller birds look for cozy houses that require less nesting material. The entrance hole size also is vital to the preferences of many species. Large birds can't fit through small holes, while small birds prefer entries they can fit through, but small enough to help deter predators.
Birds the sizes of wrens or titmice require the smallest bird houses. Construct a bird house with a 4-by-4-inch floor and a height of about 6 inches. The size of the hole varies a bit between species and ranges from just 1 inch in diameter for wrens to about 1 1/4 inches for the titmouse and 1 1/8 inches for chickadees. Center the hole about 5 inches above the floor of the bird house.
Medium-sized birds such as swallows, warblers, martins and flickers require bird houses with floors ranging in size from about 5-by-5 inches to 8-by-8. Martins seem to prefer rectangular bird houses with a floor size of 7-by-11 inches. The box height for bird houses for the medium-sized bird population is about 11 inches. Hole sizes range from 1 1/2 inches to 2 1/2 inches, depending on the size of the bird. Place the hole centered about 9 inches above the floor of the bird house.
Cavity-nesting ducks, such as wood ducks, require special birdhouse consideration. The floors of these houses can be as large as 10-by-18 inches, with a height of up to 24 inches. A 4-inch hole about 14 inches above the floor is preferred. Placement of waterfowl nest boxes in the vicinity of water and duck habitat is critical to the birdhouse success.
Birds of Prey
Some of the smaller owls use bird houses similar in design and appearance to the song bird houses. Screech owls, kestrels and barn owls will nest in bird houses. Kestrel and screech owl bird houses should have a floor of about 8-by-8 inches, with a height of 14 inches and a 3-inch hole about 12 inches above the floor of the bird house. Larger birds of prey, osprey, hawks and great horned owl, nest on open platforms of between 24 inches and 48 inches square.