Bird Nesting Box Dimensions Chart: The Complete Size Guide for Every Species

Why Dimensions Matter More Than Decorations

You can buy the most beautifully painted birdhouse at a craft fair, and it will sit empty all season. Meanwhile, a plain cedar box with the right dimensions fills up the first week it goes up. Birds do not care about aesthetics. They care about whether the entry hole keeps predators out, whether the floor space fits their nest and brood, and whether the interior height lets their chicks grow without cramping.

Getting the dimensions right is the difference between a box that attracts your target species and one that becomes a house sparrow hotel or sits vacant. This guide gives you the exact measurements for every commonly nesting cavity species in North America, plus the mounting and placement details that make the box work in the real world.

The Universal Rules

Before you look at the species-specific chart, there are a few rules that apply to every nesting box you build or buy.

Entry hole diameter is the single most critical measurement. A hole that is even a quarter inch too large lets in competitors and predators. Drill it precisely and do not round up. Use a spade bit or hole saw for clean cuts. Floor dimensions determine whether the adult bird can build a proper nest and turn around comfortably inside. Too small and the nest gets compacted. Too large and eggs roll away from the adult during incubation. Interior height from the floor to the entry hole affects how easily predators can reach in and grab eggs or chicks. A deeper box forces raccoons and cats to reach farther, giving chicks a survival advantage.

The Complete Nesting Box Dimensions Chart

Small Cavity Nesters

Black-capped and Carolina Chickadee, Entry hole: 1-1/8 inches. Floor: 4 x 4 inches. Interior depth: 8 inches from floor to entry hole. Mount 5 to 15 feet high on a pole or tree in a semi-shaded area near woods. Chickadees prefer boxes filled with wood shavings they can excavate and remove themselves. Fill the box with shavings and let them do the work.

House Wren, Entry hole: 1 inch (the smallest standard entry). Floor: 4 x 4 inches. Interior depth: 6 to 8 inches. Mount 5 to 10 feet high near shrubs or garden edges. Wrens are aggressive nest competitors and will fill every available cavity with sticks, even boxes they do not intend to use. Place wren boxes away from bluebird boxes to reduce conflict.

White-breasted Nuthatch, Entry hole: 1-1/4 inches. Floor: 4 x 4 inches. Interior depth: 8 inches. Mount 12 to 20 feet high on a tree trunk in mature woodland. Nuthatches often smear sticky resin around the entry hole as a predator deterrent, so do not be alarmed if the hole looks messy.

Tufted Titmouse, Entry hole: 1-1/4 inches. Floor: 4 x 4 inches. Interior depth: 8 inches. Mount 5 to 15 feet high in a wooded or semi-wooded area. Titmice line their nests with soft materials and have been observed plucking fur directly from sleeping dogs, cats, and even humans.

Medium Cavity Nesters

Eastern and Western Bluebird, Entry hole: 1-1/2 inches. Floor: 5 x 5 inches. Interior depth: 9 inches. Mount 4 to 6 feet high on a metal pole with a predator baffle in an open area with low or mowed grass. Bluebirds hunt insects by dropping from a perch, so they need clear sight lines to the ground. This is the most popular nesting box in North America, and with good reason: bluebird trail programs have dramatically recovered populations.

Tree Swallow, Entry hole: 1-1/2 inches. Floor: 5 x 5 inches. Interior depth: 8 inches. Mount 5 to 8 feet high on a pole near open water or fields. Tree Swallows and bluebirds compete for boxes, but you can manage this by placing pairs of boxes 15 to 20 feet apart. Typically one species takes each box, and they coexist peacefully at that distance.

Prothonotary Warbler, Entry hole: 1-1/8 inches. Floor: 4 x 4 inches. Interior depth: 6 inches. Mount 4 to 6 feet high on a pole directly over or beside standing water in swampy woodland. This is one of only two warbler species that nests in cavities. Getting the placement right, low and near water, is essential.

Purple Martin, Entry hole: 2-1/8 inches (round) or 1-3/4 x 3 inches (crescent, starling-resistant). Floor: 6 x 6 inches per compartment. Interior depth: 6 inches. Mount 12 to 20 feet high on a pole in the most open area available, at least 40 feet from the nearest tree. Martins are colonial nesters and need multi-compartment houses or gourd clusters. East of the Rockies, they nest almost exclusively in human-provided housing.

Large Cavity Nesters

American Kestrel, Entry hole: 3 inches. Floor: 8 x 8 inches. Interior depth: 12 to 15 inches. Mount 12 to 30 feet high on a tree, building, or tall pole in open farmland or grassland. Kestrels do not build nests inside the box, so add 2 to 3 inches of wood shavings on the floor. Face the entry hole toward open habitat, not toward trees or buildings.

Screech Owl (Eastern and Western), Entry hole: 3 inches. Floor: 8 x 8 inches. Interior depth: 14 inches. Mount 10 to 30 feet high on a tree in a wooded or suburban area. Add 3 inches of wood shavings. Screech owls are surprisingly common in suburban neighborhoods and will use boxes readily. Mount the box so the entry faces away from prevailing winds and afternoon sun.

Wood Duck, Entry hole: 3 x 4 inches (horizontal oval). Floor: 10 x 10 inches. Interior depth: 22 inches. Mount 6 to 30 feet high on a pole or tree over or near water. The inside front wall must be roughened or fitted with hardware cloth so ducklings can climb out. Add 4 inches of wood shavings. Wood Duck boxes have been enormously successful in restoring populations.

Barred Owl, Entry hole: 6 x 7 inches. Floor: 14 x 14 inches. Interior depth: 22 inches. Mount 15 to 30 feet high in a mature tree in deep woodland near water. These are large boxes that require sturdy mounting. Add 4 to 6 inches of wood shavings or dry leaves.

Materials and Construction Tips

Use untreated cedar, cypress, or pine lumber at least 3/4 inch thick for insulation. Never use pressure-treated wood, plywood with exterior glue, or painted interiors. The exterior can be painted or stained in a light, earth-toned color to reduce heat absorption, but leave the interior raw. Drill four quarter-inch drain holes in the floor corners so rainwater does not pool. Cut ventilation slots or drill holes just below the roofline on both sides for airflow. Make one wall or the roof hinged for annual cleaning.

Clean boxes out every February before nesting season begins. Remove old nests, scrub the interior with a stiff brush and plain water, and let it dry thoroughly. Annual cleaning reduces parasite loads and makes the box attractive to new tenants.

Placement Summary

Entry holes should face away from prevailing winds and direct afternoon sun, typically east or southeast in most of North America. Space boxes for the same species at least 100 yards apart, except for colonial nesters like Purple Martins. Different species boxes can be closer together. Always use a predator baffle on pole-mounted boxes. Try our Bird Identifier Quiz to learn which species are common in your area so you build the right boxes for your neighborhood.