Measure the dog, not the breed label.
Choose an opening that clears the shoulders and body without forcing a hard crouch or an uncomfortable step-over.
Measure shoulder height
Measure from the floor to the top of the shoulders - not the top of the head. Plan for the top of the flap to sit roughly 1–2 inches above the shoulders.
Measure body width
Measure the widest point through the chest or body and add 1–2 inches of comfortable clearance. Long hair can make the pet look wider than the body.
Check the step-over
The bottom of the opening should be low enough for the shortest, oldest or least mobile pet that will use the door.
Eleven sizes cover cats through giant dogs.
Dimensions are nominal flap-opening width × height in inches. Verify the exact selected variant and model instructions before cutting.
Size for the largest pet. Mount for the smallest.
The opening must clear the largest pet’s shoulders and body, while the step-over remains manageable for the smallest pet. Test a proposed opening with a partially opened door or a cardboard template before ordering.
- Measure every pet that will use the opening
- Account for older pets and mobility limitations
- Choose single flaps for lower resistance when needed
- Use double flaps for increased exterior weather control
Answers before you choose a size.
Keep pet measurements, rough openings and complete frame dimensions separate.
What measurements matter for a dog door?+
Measure shoulder height, body width and step-over. The flap should clear the shoulders and body without forcing a crouch, while the bottom edge stays manageable for the shortest or least mobile pet.
Should I use breed weight to pick the size?+
Breed and weight ranges can help narrow the list, but the final size should come from the individual pet's height and width.
What is the difference between flap opening and rough opening?+
The flap opening is the clear passage the pet uses. The rough opening is the prepared hole for installation. The full outer frame is larger again, so all three dimensions must be kept separate.
Which pet should I measure if I have multiple pets?+
Size the clear opening for the tallest and widest pet, then mount the door low enough for the smallest or oldest pet to step through comfortably.
When do I need a custom size?+
Consider custom sizing when a standard flap opening is too short, too narrow, too wide, or when an existing opening does not match a standard product relationship.
Should I cut before the product arrives?+
No. Confirm the exact selected model, size, rough opening and outer frame before making any permanent cut.