Knowledge base: Nest boxes and nesting birds
What size hole does a nest box need?
It depends on the bird you want. The BTO gives 25mm for blue tits, coal tits and marsh tits; 28mm for great tits and tree sparrows; and 32mm for house sparrows and nuthatches. For starlings it suggests a box with a 45mm hole. Robins use an open-fronted box instead.
The BTO sizes
| Entrance hole | Birds the BTO names |
|---|---|
| 25mm | Blue tit, coal tit, marsh tit |
| 28mm | Great tit, tree sparrow |
| 32mm | House sparrow, nuthatch |
| 45mm | Starling |
The BTO’s buying page adds that a 32mm hole suits sparrows and tits, and that 28mm is only for restricting a box to blue tits.
Open-fronted boxes
Not every garden bird uses a hole. The BTO lists pied or white wagtail, robin and spotted flycatcher as users of open-fronted boxes, which have a much larger opening than a hole-fronted box.
Other details that matter
The BTO says skip the perch, which can give squirrels or weasels a foothold, and use wooden walls at least 15mm thick. More is in when should I put up a nest box?
Sources
- BTO: Make a nest box, opened 14 November 2026.
- BTO: Putting up a nest box, opened 14 November 2026.
- BTO: Buying a nest box, opened 14 November 2026.
- BTO: Nest boxes, opened 14 November 2026.