Birdhouse Dimensions Calculator 2026
The entrance hole diameter decides which bird moves in. A bluebird needs 1½ inches; a chickadee 1⅛; a flicker 2½. Pick your species below and this free calculator gives you the exact hole size, floor size, box depth, entrance height and mounting height — plus the mistakes that make a box unusable.
Last updated: August 2026 · Dimensions follow the standard nest-box specifications published by North American ornithology and state wildlife extension programmes.
How are birdhouse dimensions decided?
A nest box is not one-size-fits-all. Four numbers do the work, and the first one matters most:
entrance hole diameter → selects the species | floor area → fits the brood | hole height above floor → keeps chicks safe from reaching predators | mounting height → matches natural nesting habitsWorked example
For an Eastern Bluebird: a 1½ inch hole is wide enough for the adult but too small for a European Starling, which is the single most destructive competitor for bluebird boxes. The floor is 5×5 inches, the box is 8–12 inches deep, and the hole sits 6–10 inches above the floor so a raccoon reaching through the entrance cannot touch the nestlings below. Mount it 5–10 feet up on a smooth metal pole with a baffle.
Nest box dimensions for common US species
| Species | Hole diameter | Floor | Depth | Hole above floor | Mount height |
|---|---|---|---|---|---|
| Eastern Bluebird | 1 1/2 in | 5 x 5 in | 8–12 in | 6–10 in | 5–10 ft |
| Western / Mountain Bluebird | 1 9/16 in | 5 x 5 in | 8–12 in | 6–10 in | 5–10 ft |
| Tree Swallow | 1 3/8 in | 5 x 5 in | 6–8 in | 4–6 in | 5–15 ft |
| House Wren | 1 1/8 in | 4 x 4 in | 6–8 in | 4–6 in | 5–10 ft |
| Carolina Wren | 1 1/2 in | 4 x 4 in | 6–8 in | 4–6 in | 5–10 ft |
| Black-capped Chickadee | 1 1/8 in | 4 x 4 in | 8–10 in | 6–8 in | 5–15 ft |
| Carolina Chickadee | 1 1/8 in | 4 x 4 in | 8–10 in | 6–8 in | 5–15 ft |
| Tufted Titmouse | 1 1/4 in | 4 x 4 in | 8–10 in | 6–8 in | 5–15 ft |
| White-breasted Nuthatch | 1 1/4 in | 4 x 4 in | 8–10 in | 6–8 in | 5–20 ft |
| Downy Woodpecker | 1 1/4 in | 4 x 4 in | 8–10 in | 6–8 in | 5–20 ft |
| Hairy Woodpecker | 1 1/2 in | 6 x 6 in | 12–15 in | 9–12 in | 8–20 ft |
| Red-bellied Woodpecker | 2 in | 6 x 6 in | 12–14 in | 9–12 in | 8–20 ft |
| Northern Flicker | 2 1/2 in | 7 x 7 in | 16–18 in | 14–16 in | 6–20 ft |
| Great Crested Flycatcher | 1 3/4 in | 6 x 6 in | 8–10 in | 6–8 in | 8–20 ft |
| Prothonotary Warbler | 1 1/8 in | 5 x 5 in | 6 in | 4–5 in | 4–8 ft |
| Purple Martin | 2 1/8 in | 6 x 6 in | 6 in | 1–2 in | 10–20 ft |
| House Finch | 2 in | 6 x 6 in | 6 in | 4 in | 8–12 ft |
| Eastern Screech-Owl | 3 in | 8 x 8 in | 12–15 in | 9–12 in | 10–30 ft |
| Northern Saw-whet Owl | 2 1/2 in | 6 x 6 in | 10–12 in | 8–10 in | 12–20 ft |
| American Kestrel | 3 in | 8 x 8 in | 12–15 in | 9–12 in | 10–30 ft |
| Wood Duck | 4 x 3 in oval | 10 x 10 in | 24 in | 16–18 in | 10–20 ft |
| American Robin (open shelf) | Open front | 7 x 8 in | 8 in | Open | 6–15 ft |
| Barn Swallow (open shelf) | Open front | 6 x 6 in | 6 in | Open | 8–12 ft |
Five mistakes that make a birdhouse unusable
- A perch below the hole. Cavity nesters never need one. It only helps House Sparrows and predators get a grip. If your box has one, remove it.
- The hole is too big. Going up even a quarter inch can let starlings in. When in doubt, go smaller — you exclude competitors, not the target species.
- No way to open it. A box you cannot clean becomes a parasite reservoir. You need a side or roof panel that swings or lifts.
- Treated or painted wood inside. Use untreated cedar, cypress or pine, ¾ inch thick. Never pressure-treated. Never paint the interior or the hole rim.
- Mounted on a tree or fence. Raccoons, cats and snakes climb. A smooth metal pole with a baffle underneath is worth more than any other single upgrade.
Where to face the entrance
Point the hole away from prevailing wind and driving rain — in most of the US that means facing east or north-east, which also keeps the box from overheating in afternoon sun. Give the entrance a clear flight path with no branches directly in front, and keep boxes for the same species at least 100 yards apart, since most cavity nesters are territorial. Tree Swallows are the exception and will tolerate a paired box a few feet away.
Gear for a nest box that actually gets used
Correct 1½ inch hole, ventilated, opens for cleaning, no perch.
Check price on Amazon1⅛ inch hole with a 4×4 floor — the right size for the smallest cavity nesters.
Check price on AmazonStops squirrels and woodpeckers enlarging the entrance and ruining the box.
Check price on AmazonA smooth pole with a baffle defeats raccoons, cats and snakes.
Check price on AmazonAs an Amazon Associate, Birdiy earns from qualifying purchases at no extra cost to you. Full disclosure.
Frequently asked questions
What size hole does a bluebird house need?
1½ inches for Eastern Bluebirds, 1 9/16 inches for Western and Mountain Bluebirds. Never larger — a bigger hole lets starlings take the box.
Why shouldn't a birdhouse have a perch?
Cavity nesters grip the entrance directly. A perch only helps predators and House Sparrows reach inside.
How high should I mount it?
5–10 ft for bluebirds and swallows, 5–15 ft for chickadees and nuthatches, 10–30 ft for screech-owls and kestrels. A baffled metal pole matters more than exact height.
What wood should I use?
Untreated cedar, cypress or pine at least ¾ inch thick. Never pressure-treated, never painted inside.
Does it need ventilation and drainage?
Both. Vent holes near the top of the side walls, and drainage holes or cut corners in the floor.
When do I clean it out?
After each brood fledges, and always before the next nesting season. That's why an opening panel is essential.
How do I keep House Sparrows out?
Hole size stops starlings but not sparrows. Mount boxes away from buildings and feeders, skip perches, and monitor regularly.
Related guides
Nest Box Designs by Species
Full build plans and design notes for each backyard species.
Read guide → 📍Choosing & Placing Nest Boxes
Where to site a box so birds actually find and use it.
Read guide → 🥚Bird Egg Identification Chart
Found eggs in your box? Identify them by colour and markings.
Read guide →