The short answer
Measure your cat's widest point (usually the shoulders or belly) and height from belly to shoulder, then compare with the flap opening, not the outer frame. SureFlap's Microchip Cat Flap opens 4 3/4 in high by 5 5/8 in wide; its larger Pet Door opens 6 11/16 by 7 in.
Opening sizes
| Flap | Opening |
|---|---|
| SureFlap Microchip Cat Flap / DualScan | 4 3/4 in H x 5 5/8 in W |
| SureFlap Microchip Pet Door | 6 11/16 in H x 7 in W |
| EASY JOY 4-Way | 5.9 in W x 6.1 in H |
| Ideal Perfect Pet (medium) | 7 x 11.25 in flap |
| Wordcam X-Large interior | 8.5 x 8.7 in |
Door and wall thickness
- Self-lining flaps fit doors up to a stated thickness (Cat Mate electromagnetic: 60 mm).
- Walls need tunnel liners or extenders, such as SureFlap's Pet Door extender.
- Glass needs a glazier and a glass-rated flap.
Big cats
For large breeds, consider SureFlap’s Microchip Pet Door or, indoors, Wordcam’s X-Large door for cats 14–30 lb.
Products mentioned
Questions readers ask
Which measurement matters most?
Your cat's widest point compared with the flap opening.
What about Maine Coons?
Look at larger openings like SureFlap's Pet Door.