Step 1:
Measure your pet from the top of the shoulders to the chest, just behind the front legs. Then measure the width of your pet at the widest point.  This will be either the shoulder or hip area.

Step 2:
Determine your pet's weight.

Step 3:
Select the correct door size based on your pet's measurements and weight.  See the chart

Step 4:
Do not pick a dog door using only your dogs weight. Measure your dog to make sure they will fit.

Helpful Tip: Get a large piece of cardboard and cut an opening the size of the flap. See if your pet is able to get through this opening. If you get the width right you will be able to adjust the height when you install the door.

Size of door

Size of flap width x length

Maximum width of pet

Weight of pet

Cat Flap

6" x 6"

5-1/2" 

12 pounds

Small

5" x 7"

4-1/2"

10 pounds

Medium

7" x 11"

6-1/2"

25 pounds

Large

9" x 15 "

8-1/2"

40 pounds

Ex Large

10-1/2" x 15"

10"

70 pounds

Super Large

15" x 20"

14-1/2"

120 pounds