Facts About Sliding door jammer UncoveredThere's your minimum width. Do not buy a flap that isn't a minimum of that large. Determine the flap height and step-over measurements you need. Ideally, the top of the flap will be at least as tall as the top of the family pet at his 'withers' (top of his shoulders). That way, he does not need to crouch to use the family pet door.That's how much he has to step over. So, flap height plus step-over is the height of the top of the flap. Generally, the...