Instructions
Measure the height of your dog from the top of the shoulder to the bottom of the chest. Your dog can be standing or sitting when you do this. When the dog enters the door, the head will go down and the legs will step over the bottom part of the door, so there will be no need to include the head and legs in the measurement.
Measure the width of your dog. Hold the tape measure from one side of the chest to the other.
Write down the measurements. Add a few extra inches to make sure there will be enough room for the dog to fit through the door. If your dog is not fully grown, then you might want to wait until then or make an approximation. This might lead you making a larger door later.
Weigh your dog. Make sure the dog isn't leaning on you and the dog is completely on the scale. Taking the dog's weight is another way to measure what size door is needed, but it isn't as accurate as taking the measurements. For example, if your dog weighs 30 to 40 pounds then use a large-size door, which is 10 inches by 15 inches.
Take the measurement from the feet to the bottom of the dog's chest. This will be how far the door needs to be from the floor and where the doggy door will need to begin.
How to Measure a Dog for a Door
A door for a dog usually is seen at the lower part of the back door to a house and sometimes through a wall near the door. There is a flap that covers the small door, allowing the dog to go in and out as needed. The doggy door serves as a great convenience, especially for busy owners. If the door is not big enough, it could hurt the dog's back and irritate the skin.