Sizing Guide & How To Measure

Internal Door Measuring Guide

Internal Doors are supplied in industry standard sizes and in most cases can be made to an exact measurement with our made to measure range. The starting point is always to measure the opening that you have (i.e. the size of the space where the door will go). 

When you are working out the door size remember that there needs to be a 2 – 4mm gap around the door to allow it to open and close and so selecting the correct door and fitting it is more of an art than a science. Also allow for the fact that doorways are typically built by human beings and so may not be exactly square and true, it is best to measure in a couple of places and take an average, don’t worry about the variation, it’s why our doors can be adjusted.

Can I measure the door that’s in the hole already?

The simplest way to measure the door that you need is to measure the old one if it’s still hanging but remember to check that it fits properly and doesn’t rub on the frame or have huge gaps around the sides and tops. If you are happy with the way the existing door is fitted then go ahead and measure it and then make your selection, if in doubt or if you are going to be upgrading the frame, measure the hole in the wall instead.

Measuring the hole in the wall

The opening that you have in the wall will either already have a frame fitted or will just be a bare opening, when you measure a bare opening the size you have is known as the “Brick to Brick opening”, or “Brick opening”.

If you are measuring an opening that already has a frame fitted, then this measurement would be described as “frame to frame”.

If you have a brick to brick opening measurement, the simplest way forward would be to contact one of our Door Experts and let them confirm the door size that is best for you.

Once I know the size, what’s next?

You may refer to the list of popular Internal door sizes, to determine the most suitable option.

If you find your sizes are close then that’s great, remember all doors can be trimmed to match your opening size and to allow for that all important tolerance that is required to ensure the doors open and close perfectly.

Standard Internal Doors

Typically, our internal door range can be adjusted down in size by 6mm on all edges to allow for a proper fit, so 12mm on the width and at least 12mm on the height can be removed to allow for fitting. In most cases the height can be trimmed more, but the maximum trimming allowance for each door can be found within the specification tab on each product page.

Fire Doors

Adjusting fire doors can be a little more tricky and accurate measurements are key. Fire doors can only be trimmed by a maximum of 3mm on any edge. Trimming more than 3mm on each edge will invalidate the fire certificate. Another thing to note when fitting fire doors is to allow for the intumescent strips, which are mandatory and should be placed in the frame or door edge, it is required that the gaps around the door are no more than 2-4mm for the strips to operate correctly.

Adapta-Door range

Our Adapta-Door range is perfect for those special situations where a standard size doesn't quite fit. With a stocked selection of doors in non-standard sizes, you can get exactly what you need without ordering a made-to-measure or bespoke product.

These styles are available in standard widths and a range of non-standard widths of 650mm, 750mm, 780mm, and 800mm, all with extra lipping to allow a trimming allowance of up to 14mm off any edge for standard doors or 12mm off any edge for FD30 fire doors.

Do I need a made to measure size door?

It is very unusual for someone to need us to build a door to a non-industry standard size if it is replacing an existing door. Our aim is always to find you the most cost-effective way to source and fit a door. If all else fails we can reach into our bag of tricks and find a bespoke solution, but we rarely have to, we have a far wider range of door sizes available to us than most, and we can typically find you a solution.

But, if all else fails, and none of our standard range will fit, even after trimming, then why not get a door made to the exact millimetre. Most of our internal door range can be made to measure. 

If you are stuck and unsure, our Dedicated Door Experts are on hand to help with any information you need. Simply use our LiveChat to speak with us right away, or alternatively call us on 0800 633 5050, or email us at enquiries@todd-doors.co.uk.