Measure the width, height, and depth of your existing door frame before you order

The most common mistake is measuring the door itself instead of the frame opening. Your replacement door must fit the frame that's already in your wall, not the other way around. You need three measurements: the width of the opening, the height of the opening, and how deep the frame sits in the wall. Take each measurement three times at different spots—top, middle, and bottom for width and height—because older frames are often slightly out of square.

Use a steel tape measure, not a cloth one. Cloth measures stretch and give you false readings. Measure in inches, and write down the smallest number you get for width and height—that's the actual opening size. If your measurements vary by more than a quarter-inch, your frame is out of square, and you'll need to tell the door supplier when you order.

Key Takeaways

  • Measure the frame opening, not the door itself, and take three measurements at top, middle, and bottom to catch frames that are out of square.
  • The smallest measurement you get is the one that matters, because your new door has to fit through the tightest spot.
  • Measure depth from the inside face of the frame to the outside face to know whether your door will sit flush with your wall or need trim adjustment.
  • Write down whether the frame is wood or metal and whether the hinges are on the left or right when you're standing outside looking in.
  • If measurements vary by more than a quarter-inch, tell your supplier—they may need to adjust the frame or the door to fit properly.

Measure the width of the frame opening

Stand inside the room and look at the frame. The frame is the wood or metal border that sits in the wall around the door. Measure from the inside edge of the left side of the frame to the inside edge of the right side of the frame. Do this at the top of the frame, in the middle, and at the bottom. Write all three numbers down.

If the top and bottom measurements are different, your frame is out of square—common in older houses. Use the smallest number as your width. If the difference is more than half an inch, mention it to your door supplier before you order, because they may recommend shimming the frame or ordering a door that's slightly smaller.

Measure the height of the frame opening

Measure from the bottom of the frame (where it meets the floor or threshold) to the top of the frame. Measure on the left side, in the middle, and on the right side. Again, use the smallest number. Most residential doors are 80 inches tall, but some older homes have 78-inch frames, and some newer construction uses 84 inches, so this measurement matters.

If you're replacing an exterior door and there's a threshold (a raised piece at the bottom), measure from the top of the threshold, not the floor. If you're replacing an interior door, measure from the finished floor to the top of the frame. The threshold or floor surface you measure from is the surface your new door will sit on.

Measure the depth of the frame in the wall

This measurement tells you how much space you have from the inside face of the frame to the outside face. Stand inside and measure from the inside edge of the frame (the part you see when the door is open) straight back to where the frame ends on the outside of the wall. This is usually between 4.5 and 5.5 inches for exterior doors and 4 to 4.5 inches for interior doors.

Depth matters because it determines whether your new door will sit flush with your wall or whether you'll need to add trim. If your new door is thicker than your old one, or if the frame is shallower than standard, the door may stick out slightly. Your supplier can tell you whether the door you're ordering will fit your frame depth, so have this number ready when you call.

Check the hinge side and swing direction

Stand outside the room looking at the closed door. If the hinges are on your left, it's a left-hand door. If they're on your right, it's a right-hand door. Write this down. Also note whether the door swings into the room or out of the room—this is the swing direction, and it matters for interior doors especially, because you want the new door to open the same way the old one did.

For exterior doors, note which side the lock is on and whether there's a storm door or screen door attached. If you're replacing a door that has sidelights (windows beside the door), measure those separately and tell your supplier, because sidelights may need to be ordered with the door as a unit.

Inspect the frame material and condition

Look at what your frame is made of—wood, aluminum, or vinyl. Wood frames are standard in most homes. If your frame is damaged, rotted, or severely out of square, your supplier may recommend replacing the frame along with the door. Take a photo of the frame and any damage and bring it or send it to your supplier before you order.

Check whether the frame has a brick mold (the trim that sits against the outside wall on exterior doors). If it does, you may be able to reuse it, or you may need to order a new door with brick mold included. Ask your supplier whether your frame can accept a standard replacement door or whether you need a custom fit.

Record all measurements on a diagram

Draw a straightforward rectangle on a piece of paper to represent your door frame. Write the width measurements (top, middle, bottom) along the top and sides. Write the height measurements (left, middle, right) along the left and right edges. Write the depth measurement inside the rectangle. Add notes about hinge side, swing direction, frame material, and any damage or unusual features.

Take a photo of your frame with your phone and keep it with your measurements. When you contact a door supplier, you'll have everything they need to confirm that a standard door will fit, or whether you need something custom. Having this information ready speeds up the ordering process and reduces the chance of ordering a door that doesn't fit.

Frequently Asked Questions

What if my measurements are different at the top and bottom?

Your frame is out of square, which is normal in older homes. Use the smallest measurement—that's the actual opening size. Tell your supplier the variation so they know whether to adjust the frame or order a slightly smaller door. A difference of a quarter-inch or less usually isn't a problem.

Do I measure the frame or the door that's already there?

Measure the frame opening, not the door. The frame is the border in the wall. The door itself may be warped or may have been installed with gaps, so it won't give you an accurate opening size. Your new door has to fit the frame, not the old door.

What if my frame is damaged or rotted?

Take a photo and show it to your supplier. Rotted wood frames usually need to be replaced along with the door. Your supplier can tell you whether the damage is bad enough to require frame replacement or whether it can be repaired and sealed before the new door goes in.

Does the depth measurement matter if I'm just replacing the door?

Yes. If your new door is thicker than your old one, it may stick out beyond the frame and wall surface. Knowing the depth ahead of time lets your supplier tell you whether you'll need to add trim or whether the door will sit flush. It also affects whether the door will close properly.

Should I measure in inches or centimeters?

Use inches. Door frames and doors in North America are sized and sold in inches. Your supplier will expect measurements in inches, and standard door sizes (like 32 inches wide or 80 inches tall) are all in inches.