How to Measure a Door Opening Before Ordering a Replacement Door

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To measure a door opening, record the width and height at several points, using the narrowest width and the shortest height as your reference, and note whether the door swings in or out and which way. Measure the actual opening rather than relying on the original door, because older frames are often out of square. Send these measurements with photos so the workshop can plan the frame and fitting correctly.

Why Accurate Measurements Matter

A custom door is made to fit one specific opening. If the measurements are off by even a few millimeters, the door may not close smoothly, may not seal against drafts, or may need costly rework. Taking the time to measure carefully at the start saves delays for everyone involved.

Your opening is rarely a perfect rectangle. Walls settle, plaster adds thickness, and old frames can drift out of square over the years. That is why the measuring method matters as much as the numbers themselves.

Tools You Need Before You Start

Prepare a few simple tools so the measurements are reliable and easy to repeat.

A steel measuring tape, preferably 5 meters long
A spirit level or a long straight edge
A notebook or your phone for recording numbers
A camera for clear photos of the opening and surroundings

A flexible cloth tape can stretch and give false readings, so a steel tape is the better choice.

Measuring Width and Height

Measure the width at the top, middle, and bottom of the opening. Use the smallest of the three readings, because the door must pass through the narrowest point. Do the same for height, measuring at the left, center, and right, and use the shortest result.

Measure from one finished surface to the other, meaning from the inside edge of the frame or wall lining to the opposite inside edge. Write down every reading, even when they match, so the workshop can confirm the opening is square.

Checking Squareness and the Floor

Compare the two diagonals of the opening. If they are not equal, the frame is out of square, and the door must be built to suit the actual shape rather than an ideal rectangle. Note this difference in your message.

Also check the threshold. If the floor slopes or is uneven, measure the gap at the bottom at both sides. Mention any tiles, carpet, or planned floor finish, since a change in floor height affects how the door clears the ground.

Recording Swing Direction and Hardware

Decide which way the door will open and write it down clearly. Stand outside the room and note whether the hinges will be on the left or right, and whether the door pushes in or pulls out.

Hinge side: left or right, as seen from outside
Opening direction: inward or outward
Existing locks, handles, or cylinders you want to keep

Knowing the hardware in advance helps the workshop plan the frame, lock position, and any reinforcement.

Sending Your Measurements and Photos

Once you have your figures, send them together with several photos: a wide shot of the whole opening, a close view of the hinge side, and a photo of the floor and threshold. Label your measurements clearly, for example "width at bottom 92 cm", so nothing is misread.

The workshop will review your information, may ask follow-up questions, and then prepare a drawing and written specification for your approval before production begins. Exact technical values and fitting details are confirmed with the workshop's engineer during this stage.

Frequently asked questions

Should I measure the old door or the opening?

Always measure the opening itself, because the old door may have been installed incorrectly or may no longer fit the frame. The opening shows the real space the new door must fill.

What if my measurements are slightly different at each point?

This is normal in older buildings. Record every reading and let the workshop know, so the door can be planned for the actual shape of the opening.

Do I need to measure the frame thickness?

Yes, note the depth of the wall or frame if you can. It helps determine how the door and frame will sit within the wall.

Can I send photos instead of visiting?

Photos help a great deal, but on-site measurement is part of the process for accuracy. Your photos and written figures will guide the initial inquiry.

Common mistakes to avoid

Avoid measuring only once, using a flexible cloth tape, or forgetting to note the swing direction. These errors are the most common reasons a door does not fit the first time.

Our recommendation

Take every measurement twice, use the narrowest width and shortest height, and check the diagonals so the workshop knows whether the frame is square.

Summary

Accurate measurements taken at several points, along with the swing direction and clear photos, give the best start for a custom door that fits well.

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