How to measure for a composite door

Send us your measurements before you order and we will sanity check them for free. It costs us five minutes and it has saved a lot of people a door that does not fit.

What you are measuring

You are measuring the structural opening, brick to brick, not the door you are replacing and not the existing frame. The old frame may have been fitted badly, may be a different size, and will be coming out anyway.

If the existing frame is staying in place, or the opening has a plastered reveal you are not removing, say so when you order because it changes what we need from you.

Measuring the width

1. 1Measure across the opening from brickwork to brickwork at the top of the opening.
2. 2Measure again across the middle.
3. 3Measure again near the bottom, just above the threshold.
4. 4Write down all three. Use the smallest of the three as your width.

Measuring the height

1. 1Measure from the underside of the lintel or head of the opening down to the finished floor or step level, on the left hand side.
2. 2Measure again in the middle.
3. 3Measure again on the right hand side.
4. 4Use the smallest of the three as your height.

Measure to the level the door will actually sit on. If you are laying tiles, a new step or a threshold ramp afterwards, that changes the height and it needs to be accounted for now, not later.

The mistakes people actually make

• Measuring the old door instead of the opening. The old door is smaller than the opening by the width of its frame on all sides.
• Measuring in one place only. Very few openings in British houses are square, and the difference top to bottom is often 8 to 15mm.
• Using the largest measurement instead of the smallest. The door has to pass through the tightest point.
• Forgetting the floor finish. A 12mm tile plus adhesive is 15mm off your height.
• Rounding up to a neat number. Give us the actual millimetres and let us handle the tolerances.
• Measuring a bowed or damaged opening without saying so. Tell us and we will advise, rather than building a door for an opening that needs making good first.

Fitting tolerance

The manufacturer takes a deduction off your stated opening size so there is room to pack and seal the frame. You do not need to make that deduction yourself. Give us the true opening size and tell us it is the opening size — the single most common way a door ends up too small is somebody deducting the tolerance twice.

Fitting notes

• Fit the frame square and plumb, and check the diagonals before you fix anything.
• Pack solidly behind every fixing point, and always directly behind the hinges and the lock keeps. An unpacked keep will pull and the door will stop locking.
• Do not over tighten the fixings. It is very easy to bow a frame and bind the door.
• Check the door opens, closes and locks smoothly before you seal and make good.
• Adjust the hinges and keeps to get an even gap all round. Hinges are three way adjustable for exactly this reason.