Before you start shopping for a new door or set of doors, you may want to measure your door to get a rough estimate of your door size. Understanding the proper way to to measure your door for replacement is important so you know what to look for when selecting your replacement door. Once you’ve got an idea of how much room you have, you can visit a showroom to view your replacement options. Before ordering or purchasing your door, it’s still a good idea to have a professional measurement, just so there are no surprises on installation day.
Hinged door measurement
First we’ll go over how to measure a door size for a typical hinged door. Generally, the rules for measurement are similar for entry doors and internal doors—that’s the heavy, insulated doors that lead outside and the lighter doors between rooms, closets, etc.
You’ll want to measure these from ‘inside’ of the door, the side with the hinges. To measure width, measure across the center horizontally from one side of the door panel to the other. Do the same for the height of the door panel. If you’re worried that the door is warped or otherwise imperfect, grab additional measurements from near either edge to see how they match up against your two center measurements.
Only measure the door here—the actual panel that swings back and forth. Round your measurements up to the nearest inch, never down; a door that’s a smidge smaller than your current door works fine, a door that’s a tiny bit larger may not fit at all.
You’ll also want to get two other measurements: the thickness of the door, and the width of the door jamb. The door’s thickness is simply the measurement of the edge of the door. The door jamb can be a little trickier, as your measurement needs to exclude any trim; you’re only measuring the wooden frame that actually holds the door up, not any of the extra bits.
As for how to measure a door frame: stand inside the open door facing the jamb. Measure from the inside edge of the trim on one side to the inside edge of the trim on the other side to get your jamb width if there’s trim installed, or simply measure the jamb if it’s unadorned.
Sliding door measurements
You’ll want to measure sliding doors from outside of your home, looking at the exterior of the door. That’s the side without the lock if it’s not an entry door and you’re not sure which side is the exterior.
You’ll want to measure the width of the door at the center, running your tape measure from siding to siding, stucco to stucco, brick to brick, whatever material outlines the sides of your sliding door. Measure vertically the same way, from where the header meets the rest of the home to where the bottom sill ends.
To put it another way, you need to know how to measure the door opening in your home when measuring for a sliding door—unlike a hinged door, a sliding door fills the entire opening, rather than leaving a significant gap to be accounted for with weather stripping and trim.
It's worth noting that these instructions for sliding door measurements also apply to certain special hinged door configurations—this is how to measure a front door with sidelights, too, as you need to know what size door for the rough opening.
What should I do with these door measurements?
Now that you have your door measurements, you’re ready to take your information and start shopping for a new door. If you take these measurements to a showroom, you’ll be able to receive a high-level quote for the door replacement. You can still have measurements taken professionally—this will give you insight into more significant changes you might make to accommodate other door types or if you’re considering making a change from a sliding door to French doors.