Measure the height, width, and depth of your current door frame before you order a replacement
Door replacement starts with three measurements: the height and width of the opening itself, and the depth of the frame (how thick the wall is). These three numbers tell you what size door will fit. Most interior doors are 32 inches wide and 80 inches tall, but your opening may differ, and the frame depth affects which replacement doors you can use. Measure twice — a mistake here means ordering a door that won't fit.
You will need a tape measure, a notepad, and about ten minutes. Take measurements from inside the house, not outside. If the frame is damaged or uneven, you may need to measure in multiple spots and note where the frame is widest or tallest — this tells the installer what they are working with.
Key Takeaways
- Measure the opening height at three points (left, center, right) and use the shortest measurement, because the door must fit the tightest spot.
- Measure the opening width at three points (top, center, bottom) and use the shortest measurement for the same reason.
- Measure the frame depth (the thickness of the wall) because it determines whether you need a standard or special replacement frame.
- Write down the measurements and note whether the frame is square, tilted, or damaged — this information helps the installer plan the job.
- If the frame is very uneven or damaged, a professional can assess whether the opening needs adjustment before a new door goes in.
How to measure the height of the opening
Use your tape measure on the inside of the frame, from the floor to the top of the frame opening. Measure at three points: on the left side, in the middle, and on the right side. Write down all three numbers. Use the shortest of the three — this is the actual height of the opening, because the door must fit through the tightest spot.
If the floor is uneven (common in older homes), measure from the highest point of the floor, not the lowest. The door needs clearance at the highest spot or it will drag. If the floor slopes noticeably, tell the installer — they may need to shim or adjust the frame during installation.
How to measure the width of the opening
Measure from the left side of the frame to the right side, again from inside the house. Measure at three points: at the top, in the middle, and at the bottom. Write down all three. Use the shortest measurement — this is your actual opening width.
If the frame leans inward or outward (not square), the top and bottom widths will differ. This is common and not a problem for replacement, but the installer needs to know. Write down which measurement is smallest and note that the frame is not square.
How to measure the frame depth
Frame depth is how thick the wall is. Stand inside the house and look at the edge of the frame where it meets the wall. Measure from the inside face of the frame (the part you see from inside the room) to the outside face (the part you would see from outside). This is your frame depth.
Standard frames are usually 4.5 to 5 inches deep, which fits a typical 2×4 wall with drywall on both sides. If your wall is thicker (common in older homes or exterior walls), the depth may be 5.5 to 6.5 inches. If it is thinner (some interior walls), it may be 3.5 inches. Write this number down — it tells you whether you need a standard replacement frame or an extension jamb (an extra piece that fills a thicker wall).
What to do if the frame is damaged or uneven
If the frame is warped, cracked, or rotted, you still measure the opening itself, but note the damage on your measurement sheet. A damaged frame may need repair or replacement before the new door goes in, which is a separate job from the door itself.
If the opening is very uneven — for example, the top is 2 inches narrower than the bottom — the frame may need to be squared up during installation. This is normal and the installer will handle it, but it is worth mentioning when you order so they know to plan for it. Take a photo of the frame from the side if it looks tilted; this helps the supplier or installer see what they are dealing with.
Recording your measurements correctly
Write your measurements in a clear format so you do not mix them up later. A straightforward format is:
- Height: left _____, center _____, right _____ (use the shortest)
- Width: top _____, center _____, bottom _____ (use the shortest)
- Frame depth: _____
- Notes: (frame square? damaged? uneven floor?)
Take a photo of the frame from the side and from the front. These photos help a supplier or installer understand the condition of the frame and whether any prep work is needed. If you are ordering online or getting a quote, having clear measurements and photos speeds up the process.
When to call a professional to measure
If the frame is very damaged, the opening is severely uneven, or you are unsure about your measurements, a door installer can measure for you. This usually costs $50 to $150 and takes about 15 minutes. It is worth paying if the frame needs repair or if you want to be certain the door will fit — a mistake in measurement can mean returning a door and ordering again.
If you are replacing an exterior door, a professional measurement is more important because exterior frames are more complex (they involve weatherproofing and may need adjustment for proper drainage). Interior doors are more forgiving, and most homeowners can measure accurately with a tape measure and care.
Frequently Asked Questions
Do I measure the old door or the opening?
Measure the opening, not the door. The opening is what matters — the door must fit the frame. If the old door is warped or undersized, measuring it will give you the wrong number. Measure the frame opening itself.
What if my measurements are different at each point?
This is normal and expected. Use the smallest measurement for both height and width — the door must fit through the tightest spot. If the difference is more than half an inch, note it on your order so the installer knows the frame is not square and can plan accordingly.
Does frame depth matter if I am just replacing the door?
Yes. If you are replacing only the door and keeping the existing frame, frame depth tells you whether the new door will fit the frame. If you are replacing the entire frame and door together, depth still matters because it determines what size frame you order. Always measure it.
Can I measure from outside the house?
No. Measure from inside. Outside measurements include trim and siding, which will give you the wrong number. Always measure the actual opening from inside the room.
What if the floor or top of the frame is not level?
Measure from the highest point of the floor and the lowest point of the header (the top of the frame). The door needs clearance at these points. If the floor slopes or the header sags, tell the installer — they may need to shim the frame during installation to make it work properly.