Each bird needs its own entrance hole, floor size and box depth, and the right hole keeps out the bigger birds that take over nest boxes. The sizes come from the Cornell Lab of Ornithology's NestWatch program and the US Fish and Wildlife Service, and every box has the details those guides ask for: vent and drainage holes, a roof that keeps rain off the entrance, no perch, and a side that opens for cleaning.
How to use this calculator
- Choose the bird. Each one comes with its own hole size, floor, depth, entrance height and the height to mount the box.
- Enter how many boxes to build. Several boxes share the boards, so the shopping list stays short.
- Set the longest boards you can bring home, then take the shopping list to the store. The walls come from the narrowest board that fits the box, and the plan tells you which pieces to cut to width.
- Follow the steps in order: cut, drill the entrance and the vent and drainage holes, put the box together, hang the side that opens, fit the roof and mount it on a pole with a baffle.
Worked examples
A bluebird box
Bird: Eastern Bluebird
- Nest box for the Eastern Bluebird
- 1.5 in entrance hole
- Floor inside
- 5 × 5 in
- Entrance above the floor
- 7.25 in
- Mount it
- 4 to 6 ft off the ground
- Boards to buy
- 2
A house wren box
Bird: House Wren
- Nest box for the House Wren
- 1 in entrance hole
- Floor inside
- 4 × 4 in
- Entrance above the floor
- 6 in
- Mount it
- 5 to 10 ft off the ground
- Boards to buy
- 2
A chickadee box
Bird: Black-capped Chickadee
- Nest box for the Black-capped Chickadee
- 1.13 in entrance hole
- Floor inside
- 4 × 4 in
- Entrance above the floor
- 6.25 in
- Mount it
- 5 to 15 ft off the ground
- Boards to buy
- 2
Tree swallow boxes for a field
Bird: Tree Swallow · Nest boxes: 4
- Nest box for the Tree Swallow
- 1.38 in entrance hole
- Floor inside
- 5 × 5 in
- Entrance above the floor
- 6 in
- Mount it
- 5 to 6 ft off the ground
- Boards to buy
- 4
A kestrel box
Bird: American Kestrel
- Nest box for the American Kestrel
- 3 in entrance hole
- Floor inside
- 8 × 8 in
- Entrance above the floor
- 12 in
- Mount it
- 10 to 30 ft off the ground
- Boards to buy
- 2
A screech-owl box
Bird: Eastern Screech-Owl
- Nest box for the Eastern Screech-Owl
- 3 in entrance hole
- Floor inside
- 8 × 8 in
- Entrance above the floor
- 12 in
- Mount it
- 10 to 30 ft off the ground
- Boards to buy
- 2
Why each bird needs its own hole
The entrance hole decides who moves in. A hole of 1.563 inches or more lets in European Starlings, and House Sparrows fit through 1.25 inches. Both are aggressive non-native birds that take over boxes, so NestWatch suggests the smallest hole the bird you want can use.
That is why a house wren box gets a hole of only 1 inches, a chickadee box 1.125 inches, and an Eastern Bluebird box 1.5 inches. Kestrels and screech-owls need 3 inches, and a bigger box to match.
The details that keep a nest dry and safe
- Walls at least 0.75 inch thick keep the nest insulated. Use untreated, unpainted wood such as cedar, pine or cypress, and never paint the inside of the box or the entrance hole.
- Vent holes of 0.625 inch near the top of each side let hot air out, and drainage holes of 0.375 to 0.5 inches in a floor recessed 0.25 inch let water out.
- The roof hangs 2 to 4 inches past the front to keep rain out of the entrance, and the plan makes it 2 inches wider on each side when the boards allow.
- There is no perch: the birds do not need one, and it gives predators and sparrows a place to wait. The inside of the front is roughened below the hole so the young can climb out.
- One side swings open on two screws, so you can check the nest and clean the box out after each brood.
Where and how high to put it up
Each bird has its own height: an Eastern Bluebird box goes 4 ft to 6 ft up, a kestrel or screech-owl box 10 ft to 30 ft. The plan gives the range for the bird you pick.
NestWatch recommends a metal pole with a baffle rather than a tree or a fence post, which snakes, raccoons and cats climb easily. A stovepipe baffle is about 8 inches across and 24 to 36 inches long, mounted on the pole below the box.
How far apart should I put several bird houses?
Give each kind of bird its own room: allow at least 300 ft between bluebird boxes, 35 ft for tree swallows, and 100 ft for house wrens. To let bluebirds and tree swallows share a yard, pair two boxes on separate poles 15 to 25 ft apart, or mount them back to back on one pole.
Where in the yard should a bird house go?
Match the spot to the bird. Bluebirds and tree swallows like open lawn or field with scattered trees, while house wrens and chickadees do better near trees, tall shrubs or a woodland edge. Point bluebird and tree swallow boxes toward open ground, preferably east, and face chickadee boxes away from the prevailing wind, in a spot with 40 to 60 percent sun.
Common questions
What size hole does a bluebird house need?
For Eastern and Western Bluebirds, a round hole of 1.5 inches. Mountain Bluebirds are a little bigger and need 1.563 inches.
How high should a birdhouse be off the ground?
It depends on the bird: from 4 ft to 6 ft for bluebirds up to 30 ft for kestrels and screech-owls. Pick the bird above and the plan gives its range.
Should a birdhouse have a perch?
No. The birds that use nest boxes do not need one, and a perch helps predators and House Sparrows get at the nest.
What is the best wood for a birdhouse?
Untreated cedar, pine or cypress, at least 0.75 inch thick. Leave the inside bare: no paint, stain or preservative.
How big should a chickadee house be?
A floor of 4 inches on each side, a depth of 8 inches and an entrance of 1.125 inches. The third example above builds it.
How big does a bird house need to be?
It depends on the bird, and the entrance hole matters most. A bluebird box has a floor 5 inches on each side, a depth of 9 inches and a hole of 1.5 inches. A house wren box is smaller, with a floor 4 inches on each side and a hole of 1 inches. A kestrel box is much bigger, with a floor 8 inches on each side and a hole of 3 inches. Pick your bird above and the plan lists every size.
Will birds sleep in a birdhouse?
Yes, sometimes. Bluebirds, chickadees, titmice and nuthatches may shelter in a nest box on cold nights, though a box is not ideal for roosting. You can leave the box up through winter, then clean out the old nest at the end of the season.
When should I put up a bird house?
Get the box up before nesting season: by February in the South, and by mid to late March in the North. Birds can take a while to find a new box, so don't give up if it sits empty at first.