For width, ignore the frame itself. You want the rough opening—the hole in the wall where the door lives. Measure from the inside of the left jamb to the inside of the right jamb. But here’s the kicker: do it at the top, middle, and bottom. If your house is old enough to remember disco, those numbers will be different. Take the smallest width, and write it down in permanent marker on your hand so you don’t forget.
I once measured a door while wearing oven mitts because I was also making a pizza. The result was a door that looked like it was designed by a funhouse mirror. Don’t be me.
Depth is the Silent Friend
Don’t forget to measure the depth of the frame—the space from the inside edge of the track to the outside. This is where sliding glass doors are like pancakes: they come in thin and thick varieties. A standard is about 4-7/8 inches, but your door might be a husky athlete. If you get it wrong, your new door will stick out like a sore thumb—or worse, not fit at all.
Standard Sliding Glass Door Measurements In Inches - Glass Designs
I once ordered a door that was too slim, and it left a gap big enough for a rogue squirrel to move in. That squirrel now pays rent in acorns and sass.
