Measuring Your Pet for a Pet Door
Why measure? Can't I just estimate or use my pet's weight? You want your cat or dog to reap the benefits of the freedom you're offering with a pet door, and you're buying yourself some freedom too, so make sure they can actually step up, over and through the door you select. Your pet's weight alone does not provide enough information to choose the proper pet door size! Age, agility and build are also factors. A lean dog with long legs has different needs than a short but heavy dog with the same weight.
What do I measure? There are 3 aspects of a pet door to consider:
1. Flap Size - flap width and flap height to assure the flap opening is sufficiently large.
2. Door Height/Installation Height - Mounting the door at a proper height from the floor allows your pet to walk through without having to crouch, an important consideration for aging pets. It's normal, however, for pets to duck their head a bit when stepping through.
3. Rise - clearance height off the floor. This measurement tells you where the bottom of your pet door should go, and is the height your pet must step over. Tall and young dogs will have no trouble stepping over a higher rise, say 7" or 9", while a short or older pet might only manage a 3" rise. For wood or metal doors, you can set the rise to your pet's comfort during installation of the pet door. In sliding glass installations that employ a panel pet door, however, the rise is fixed and pre-determination is needed to select the right size. The rise is also needed to calculate shared flap height when you've got more than one pet using the door.
How do I measure?
Flap Width: Measure the widest part of your pet, usually the shoulders or hips. Add 1" to 2" for a comfortable size. Another method is to hold open a door just wide enough for your pet to get through, then measure that opening, and add 1" to 2" to arrive at minimum flap width.
Flap Height: Measure from your pet's top of shoulders (just behind his head) to the bottom of his chest (just behind the front legs), then add 1" to 2".
Door Height/Installation Height: Measure from the floor to the top of your pet's shoulders, then add 1" to 2". Ideally, the top of your pet door flap, once installed, will be at least as high as the top of your tallest pet's shoulder. This ensures that your pet can walk straight through without having to crouch.
Rise: Take the Door Height and subtract the Flap Height. The result is the rise. Double check your rise by measuring the distance between the floor and the lowest part of your pet's chest or stomach.
If you have more than one pet that will be using the same door, measure all pets. Use the height of the tallest pet for the Door Height, and use the width of the widest pet for the Flap Width. Using the Rise of the shortest pet, subtract the smallest Rise from the tallest Door Height to get the necessary shared Flap Height that will let a tall dog step through the door, while still allowing the short pet to get over the threshold.
Example: You have a Golden Retriever that's 22" at the shoulders (Door Height), who needs a Flap Height of 13". Calculate his Rise as 22" - 13" = 9". If you also have a Shih Tzu who can only manage a 5" Rise, recalculate the shared Flap Height as 22"- 5" = 17". You'll need to order a pet door with a flap size of 17" or larger to accommodate both pets. If you have pets at opposite ends of the size spectrum, e.g. a Great Dane and a Chihuahua, you may need separate doors, as the weight of the extra large flap may be too much for the tiny dog to push open.
If your pet is still growing, consider their full-grown size - you may need to consult a guide or a breeder.
If your pet has arthritis or is aging, it's doubly important to take good measurements so they won't have to struggle with climbing over a too-high threshold or crouching down to get through a too-low flap.
Selecting a Door
Find the door size that comes closest to meeting your width, height and rise needs. If in doubt, it's best to go with the larger size. For patio panel doors, choose the rise that will place the top of the flap as close as possible to the top of your pet's shoulders. (Add fixed Rise to Flap Height and see if it's equal to or greater than your dog's height at his shoulders.)
Testing your final door selection size: Cut a hole in cardboard that's equivalent to your desired pet door flap size, hold it at a height equal to the calculated rise, and coax your pet to step over and through the opening. If he can't comfortably do so, remeasure. You could also hold a board that matches your rise measurement across your doorway (you could even place duct tape across the opening) and have your pet step over it to test rise alone.