If you’re buying a pet door for the first time, you’re probably wondering: “How big of a dog door do I need?”

Getting a properly sized dog door flap is vital for the long term health and comfort of your dog and cat. This guide will help you find out what dog door measurements you will need so that your pet loves their new door as much as you.

How to Measure Your Dog For a Dog Door Contents:

• “How to Measure Dog for Dog Door” Instructional Video
• Measure Your Pet’s Width
• Measure Your Pet’s Height
• Adding a Step-Over
• Why is Measuring Correctly So Important?

Measure Your Pet's Width:

Step 1: Open your door or sliding glass door as wide as your pet needs to walk through comfortably. Using the door opening size rather than measuring your dog's width with a ruler ensures that you allow a little wiggle room for the final dog door or cat door flap size.

Step 2: Try using a treat to motivate your pet to walk through the door or sliding door opening you make.

Step 3: Measure the width of the opening you have made.

You need the flap door to be at least that wide. It doesn't need to be wider, but it should not be any narrower. Pay special attention if your dog has a particularly deep chest or is low slung and adjust your doggie door size selection accordingly. For pet owners with more than one pet, make sure that you do this with your widest and tallest pet so that the doggy door size you choose works for all your pets.

Measure Your Pet's Height:

Step 1: Have your pet stand completely upright. For multi-pet homes, make sure to do this with your largest dog or cat.

Step 2: Grab a tape measure or ruler and measure from the floor to the tallest point of your dog's back (this may be their shoulders, mid-back, or tailbone).

Step 3: Now that you have your dog's height let's factor in step-over...

Adding the Step-Over:

Step 1: Consider how high off the ground you want to install your pet door. The distance from the ground to the bottom of the pet door flap is called the "step-over."

Step 2: Add the step-over height to the height of your pet measured earlier. The top of the flap should be mounted at least 1" higher than this.

Step 3: In no case should the step-over exceed 1/3 of the height at the withers - the lower the step-over, the better. Adjust until you decide on a step-over height and dog door size that will allow at least 1" above your pet's withers.

Tip: Backyards and patios are typically a few inches lower than a home's floor level. Please make sure that your dog is comfortable stepping over both the step-over and the extra distance between the floor-level and the ground outdoors. This is more important for doors with large step overs or tiny dogs.

Note: The step-over can get a little tricky to customize for installations such as French doors or sliding doors, which may have less wiggle room for step-over height. You cannot have a dog door too high above the ground without risking the integrity of the door frame/glass.

A great customizable option for sliding glass patio doors is the Endura Thermo Panel 3e, which features user-adjustable step-over height ideal for long-legged dogs (like Great Danes and German Shepherds) or short-legged dogs (like corgis).

This patio panel insert has all the energy efficiency of the Endura Flap with the convenience of an adjustable step-over for maximum ease of use. Pay special attention if your dog has a particularly deep chest or is low slung and adjust accordingly.

Tip: You can cut a hole in a piece of cardboard the same size as the pet door you want to buy. You can then hold it up and test to see that it's wide and tall enough, the step-over is the right size, and if all your pets can fit.

If you have a larger/taller dog sharing a pet door with a smaller dog or would just like to have a taller pet door:

On the far right of the image above is a pet door with a "high aspect ratio."

The best dog door that allows for a high aspect ratio is our very own high quality, energy-efficient Endura Flap. It allows for a tall flap height for tall dogs to move through comfortably and a small step-over that small dogs can clear. Check out the size chart and browse the different sizes to choose the perfect size pet door for your pets. The high aspect ratio Endura Flaps come in sizes Small-Extra Large, so there are lots of options for selecting the step-over that works for you and your pets.

Why Is Measuring Doggie Door Sizes Correctly So Important?

Whether you have a small or large dog door, your pet door needs to be as accessible as possible for your pet. This also means ensuring that the door flap remains accessible throughout the entirety of your pet's life. Pet door sizes that were accessible to your pets during their youth may become more difficult for them as they age.

Plus, knowing how to measure for a dog door is universal between pet door types. The steps you need to take to measure your dog or cat will be the same whether you’re looking to install a pet door for walls or cat flap window insert.

So you’re probably wondering: “what size pet door do I need” and how do I know if my measurements are correct?

When comparing your pet’s measurements to a dog door size chart, make sure: 

• The top of the opening is at or above your pet’s withers, so they don’t have to crouch when they are using their door.
• The width of the door flap opening is as wide as your pet is or a little wider.
• The step-over is as low as possible while still keeping the top of the opening up at or above your pet’s withers.

A properly sized door means all you'll need to do for maintenance is purchase replacement flaps if necessary-- no need to replace the entire door assembly as your pet ages.

There may also come a time when your pet won't be able to use their pet door. Maybe they've developed hip problems or an injury. Perhaps they're just older and can't move very well.

This is when a nice and low step-over comes in handy, so they don't have to strain themselves crawling into a door that is too high off the ground for them in their old age.

This is what “high-aspect-ratio” pet doors (also known as tall dog doors) are all about. For a given width, you get more height, which means you can get the step-over lower to the ground for easier access later in life (also a great bonus for giant breeds and smaller breeds sharing).

Of course, it all depends on your unique situation. Maybe your pet is a youngster, and you're going to move to a new place soon. In that case, mount the pet door at the correct height (at or above his withers). He'll be able to use a higher step-over until you move, and you can quickly get an appropriately sized pet door at your next house.

Frequently Asked Questions

What size door do you recommend for cats?

For cats, we generally recommend the small. However, for the best results, we still highly suggest measuring your cat's height.