The key to a Blue Tit box is a small entrance hole, 26–28 mm. This is the most important difference from the Great Tit box (32–34 mm) — the smaller hole keeps out the larger and more dominant Great Tit.
| Measurement | Value | |---|---| | Entrance hole | 26–28 mm | | Internal floor dimensions | approx. 11 × 11 cm | | Height of hole above floor | 12–17 cm | | Mounting height | 2–4 m | | Aspect | entrance facing east–south-east |