Here are the key points to consider in purchasing a patio pet panel:

1. Measure the height of your sliding glass door track-  Don't just assume that 'it's standard' as they do vary. Using a ruler, measure inside the track, very top to very bottom (see the illustration in the 'Patio Panel FAQ' section). Always compare your track height to the adjustment ranges shown for the various pet doors. Some manufacturers offer custom heights for the occasional odd size. Others don't.

2. Determine how wide the flap needs to be- Open your sliding glass door wide enough for your pet to come through comfortably. Allow room for growth as needed.  There's your minimum width. Don't buy a flap that isn't at least that wide.

3. Determine the flap height and 'rise' dimensions you need-  Ideally, the top of the flap will be at least as tall as the top of the pet at his 'withers' (top of his shoulders). That way he doesn't have to crouch to use the pet door. The 'rise' dimension is the height of the bottom of the flap above the base of the pet door.  That's how much he has to step over.

So, flap height plus rise is the height of the top of the flap.

Generally, the lower the rise the better. Especially when your pet is older or arthritic, less to step over is better. So you might prefer a flap 17" tall with a 3" rise to one with a 15" height and 5" rise. Both reach 20" at the top, but the taller flap yields a lower rise.

More flap and less rise can also be helpful if you've got a small pet that needs to share with a larger one.

A pet door that incorporates a 'User Adjustable Rise' makes it simpler and offers more flexibility for the future.

4. Check the color of your framing- Most brands are available in white, satin (aluminum color) or bronze (very dark brown). You can paint any of these to get a different color if you wish but the easiest to paint is the white. Check with your local paint shop for primer and paint recommendations. The Pride panel comes in black and tan in addition to the three basic colors.

5. See if you have dual-pane glass- If you do and you're in a tough climate area, you may wish to choose a pet door that has dual-pane glass also. You can tell by placing a finger on both sides of your glass. If they look like they're touching, you have single pane. If they stop about ¹/₂" apart, you have dual pane.

However, you may choose not to as well. Single pane glass pet doors will be lighter and less expensive than dual-pane glass pet doors and will fit just as well.

6. See if you've got vinyl frames- There is more standardization in the newer vinyl framed panel doors and Ideal has taken advantage of this fact to develop a vinyl framed panel door, the VIP, that is beautiful!  Also, the Pet 1 Products patio panel will fit in a vinyl frame though it does not mate to your lock as does the VIP. It does, however, come with an effective "Charley Bar".

Of course, there are other considerations. But take a look if your frames are vinyl.