The opening size. The height from the floor. The clearance when your sliding door opens. Choosing a pet door means checking more than whether it can go in the glass.
Measure the animal, not the breed name
“Small dog” is a starting description. It is not a fitting measurement.
Use the measuring guidance on our pet-door page to record your pet’s body width, body depth and relevant heights. If more than one pet will use the door, include each of them. Tell us if one is still growing or has difficulty stepping through an opening.
Do not make a pet squeeze through an existing flap to prove that it fits. If the fit looks doubtful, stop and have the options checked.
Look at the opening the pet actually uses
The outside size of a pet door includes its frame. The usable opening inside that frame is a different measurement.
This is why two products that appear similar from a distance can suit different animals. Send the exact model you are considering, or tell us you have not chosen one yet. We can check the model information alongside the measurements you provide.
The hole in the glass is another separate measurement. Do not use an online opening dimension as a glass-cutting template.
Remember the step on both sides
The pet has to enter and leave from the floors or ground on either side. A change in level matters when considering the position of the opening.
Photograph the bottom of the glass and the surfaces on both sides. If there is a step outside, show it. If the panel slides, show the adjacent panel too.
A flap that suits the animal also needs to work with the movement of the door. An existing hole does not guarantee that a different model can be fitted without changing the glass.
Check the control you need
A larger manual pet door and a microchip model solve different problems. First Glass has manual dog-door options and SureFlap microchip options for cats and small dogs.
Do not assume that a microchip model is available in a suitable size for a larger dog. Tell us whether size, selective entry or both are important.
Start with what fits
Compare the usable openings and work through the measuring guide on our pet-door page. You can explore the options before choosing a model.
Your measurements help explain the animal and the opening. They are not final glass specifications. First Glass will confirm what needs measuring and whether replacement glass is required before work is agreed.