A bluebird box bluebirds actually use has a 1.5 inch entrance hole, a floor of roughly 4 by 4 inches, the hole set 6 to 10 inches above that floor, a side opening for cleaning, and no perch of any kind. Mount it on a metal pole in open grass and you are most of the way to occupancy. The details below are the rest.
The dimensions that decide the tenant
One and a half inches is the number that matters. It admits eastern, western, and mountain bluebirds while excluding starlings, and it is the most common error in store-bought boxes, which often drill the hole oversized for looks. Hole diameter by species is laid out in our bird house hole size chart. Skip the perch dowel entirely. Perches help house sparrows and wrens hijack the box, and bluebirds need none to enter.
Placement rules
Open grass with short vegetation, the hole facing a lawn or meadow, pole five to six feet up with a raccoon baffle below the box. Bluebirds hunt from perches into open ground, so a box at a woods edge reads as wren habitat, not bluebird habitat. Fifty to a hundred feet from cover is the usual working range. Measurements for other species are in our bird house plans with dimensions.
A buildable plan
One 6 foot 1×6 cedar board covers a single box. Cut a front 9 inches, a back 14 inches, two sides about 10 inches with beveled top edges, a 4 by 4 floor with corner drains nicked in, and a roof with a slight overhang on the front. Drill the entrance hole 7 inches above the floor, leave ventilation gaps along the roofline, and hinge one side for nest checks. Finish the outside only, or leave the wood bare.
The part most plans skip
An unmonitored bluebird box in sparrow territory becomes a sparrow factory, and house sparrows will kill sitting bluebirds. Checking the box weekly through the season and removing sparrow nests is not optional upkeep, it is the difference between raising bluebirds and feeding their competitors. The wider routine, from mealworms to water, is in our guide on how to attract bluebirds.
