Door Measuring Guide

Ordering the wrong size door is one of the easiest mistakes to make and one of the easiest to avoid. Here are 3 simple steps to measure your opening correctly before ordering, and your new door should simply fit straight in, with no surprises on delivery day.

And if you're ever unsure, call our team on 0113 450 9661 or email info@deal4doors.co.uk we're happy to assist you.

What You'll Need

• Steel tape measure (since cloth tape measures can stretch and cause errors).
• Pencil and paper or a phone to keep track of measurements.
• Another person if measuring a tall or difficult-to-measure opening.

Step 1: Measure the Height

When measuring the inside height of your existing frame of the opening, make sure to measure the frame, not the door, which might have been planed in previous years and no longer fits properly.

1. Place your tape measure against the top of the opening (the frame).
2. Measure straight to the floor or threshold.
3. Measure on the left side, on the right side, and in the middle of the opening.

Because your frame and floor may not be level, the height measurements that you get may vary slightly. So take the longest measurement because it is very easy for you to plane the new door down to be the right height after you have completed hanging it.

The majority of UK internal doors measure 1981mm high (78"), however, there are also some internal doors measuring 1982mm high and 2032mm high (80"), as well as some metric ranges at 2040mm.

Step 2: Measure the Width

Width is measured the same way, just turned on its side.

1. Measure from one edge of the frame to the other at the top, the middle, and the bottom of the frame.
2. Make a note of each entry as three separate measurements.
3. Use the widest measurement as your door width.

Your New Door will also require space to be able to open and close correctly. A good guideline is to leave an approximate gap of between 2- 3 mm on either side of your new Door and slightly more at the top.

The standard sizes for the internal UK doors are 457mm (18"), 533mm (21"), 610mm (24"), 686mm (27"), 762mm (30") and 838mm (33"). If your Door does not have an exact measurement, you do not need to be overly concerned, as many of the ranges of Doors that are available have an oversized range and a made-to-order range available and can guide you appropriately.

Step 3: Measure the Thickness

Door thickness is important for fit, weight, and, especially with fire doors, performance.

• Internal doors are normally 35mm or 40mm thick.
• Fire doors are usually 44mm thick, sometimes 54mm for high-rated commercial doors.
• External doors are normally 44mm or more to withstand the weather and give better security.

If you're keeping the old frame, measure the thickness of the door currently in it, and order accordingly. If you are also replacing the frame, then you have more flexibility to choose the door first and then fit a lining to suit.

Step 4: Check the Frame, Lining, and Architrave (If Replacing These Too)

If you’re installing a new frame or door lining, take a few extra measurements before ordering:

• Measure lining width across the total thickness of the wall, including plasterboard or finish, ensuring the lining is flush on both sides.
• Structural opening size: Approximate size of the space in the wall before a frame is fitted. Useful if you’re starting from scratch rather than replacing like-for-like.
• Architrave length measures around the full perimeter of the frame if you're ordering trim to match it.

We stock door linings, architraves, and skirting in finishes to match our internal door ranges, so if you're doing a full doorway refresh, it's worth measuring these at the same time.