The short answer
Measure your dog's body depth (top of the shoulders to the bottom of the chest) and widest point (usually the chest), and choose a flap at least an inch or two bigger in both. Then mount it so the top of the flap is at or above shoulder height, with a step-over low enough for your dog, especially seniors.
The three measurements
- Body depth: with your dog standing, top of the shoulders to the bottom of the chest.
- Width: across the widest part, usually the chest.
- Shoulder height: floor to the top of the shoulder blades; the top of the flap should sit at or above this once installed.
- Step-over: floor to the bottom of the frame; keep it well under your dog's leg length.
Reading flap sizes
| Door | Flap (maker) | Pets (maker) |
|---|---|---|
| PetSafe Plastic (Medium) | 8 1/8 x 12 1/4 in | Up to 40 lb |
| PetSafe Sliding Glass (Large) | 10 1/4 x 16 3/8 in | Up to 100 lb |
| PETCOMING XL | 24 x 15.7 in | Giant dogs |
Growing puppies and multi-pet homes
Size for the adult dog. For homes with a cat and a big dog, consider a door with a selective-entry option or two doors.
SafetyA door big enough for your dog can let in other animals; lock it at night.
Products mentioned
Questions readers ask
How much bigger than my dog should the flap be?
At least an inch or two more than body depth and chest width, mounted so the top of the flap is at or above shoulder height.
Should I size for a puppy?
Size for the adult dog.