Get the measurements wrong and you’ll end up with a door that doesn’t fit, a delayed installation, and maybe even a bigger charge than expected. Get them right, you get a perfect fit and the door you always wanted.
At The Advanced Group, we measure doors day in, day out. And while our team is always happy to carry out a home assessment, you can also measure your door yourself for an accurate starting point, saving you extra time and hassle.
Here’s how to measure a door.
What you’ll need to measure a door – By double glazed panel door professionals
The Advanced Group knows a lot about windows and doors as double glazing experts. From how to paint panel doors to fixing squeaky door noises, we have you covered. But sometimes, TLC isn’t enough to get your door up and running or looking it’s best. In this case, you may need to start thinking about getting a new one.
So let’s keep it simple.
Whatever your door type, panel door, French door, or composite. Here is everything you will need for accurate measurement of your external or internal door is:
- A rigid metal tape measure (not a fabric one, they stretch out over the years)
- A pencil and paper, or your phone to write down numbers
- A spirit level (very useful but not essential)
- Someone to hold the other end of the tape if you’ve got a tall opening
One thing before we start our guide on how to measure doors: doors must be measured in millimetres. This might sound fussy, but it gives you complete accuracy when ordering your door.
Accuracy matters when ordering doors. Rounding to the closest centimetre can leave you with gaps or a door that is too big for your brick opening.
Step 1: Measure the door width
The width of the horizontal measurement across your door opening. It needs to be taken at three points: the top, the middle, and the bottom.
Despite looking like a perfect rectangle, especially in older Scottish properties where things shift and settle over the decades, they rarely are.
If you are measuring an existing door frame (the most common scenario for a replacement), measure the inside of the frame from left to right at each of those three points. If there’s no frame and you’re measuring a bare brickwork opening, measure brick to brick across the opening.
Write down all three numbers and use the smallest one.
That’s your width measurement.
Picking any other measurement risks ordering a door that’s too wide to fit through the narrowest side of the door.
Step 2: Measure the door height
Exactly the same principle, just a different direction.
Measure the vertical distance from the bottom of the opening (or the top of the threshold) to the top of the frame. Again, in three places: left side, centre, and right side.
Pick the smallest measurement.
Something worth checking while you’re at it is whether the opening is roughly level.
If the difference between your three height measurements is more than about 5mm, the opening might be out of square. If this is the case, you should let your installer know. They will be able to find an appropriate fix to allow you to benefit from a new door.
Step 3: Measure the depth
This step gets overlooked more than it should. The depth (sometimes called the reveal or the jamb depth) is the thickness of the wall where the door sits.
Measure from the outside face of the wall to the inside face, including any render or plaster. This measurement tells your installer how deep the new door frame needs to be.
Although not every new door needs a new frame, for exterior doors, it is often recommended. This is because it ensures a tighter seal for better security and energy efficiency.
Most modern homes have a fairly standard wall thickness, but older stone-built properties in Scotland can have walls that are significantly thicker, and that affects which frame profile is needed.
If you’re replacing a door with sidelights (the narrow glazed panels that sit on either side of some front doors), measure the depth at several points. This is because the wall thickness can vary across a wider opening.
What about the existing door itself?
It is common for people to think measuring the old door is an easy way to check what will fit, but often this leads to incorrect sizes.
Wooden doors can swell and shrink with the seasons, and even the strongest of composite materials can be affected by thermal changes over years.
Your door frame or brickwork opening is the most reliable frame of reference, because it hasn’t changed shape.
That said, if you’re ordering a door to fit an existing frame that you’re keeping (rather than replacing the whole frame), then yes, measure the door slab itself.
Standard external door slabs in the UK are typically 44mm thick, but older doors can be thinner, so don’t assume you know your door thickness.
Standard sizes of new front doors in the UK
There’s no single “standard” front door size in the UK, but there are common sizes that most manufacturers work with. Looking at these can help you know whether you need to order a standard door or if you should buy something made to measure.
The most common UK external door sizes are:
- 813mm x 2032mm (2’8″ x 6’8″)
- 838mm x 1981mm (2’9″ x 6’6″)
- 920mm x 2085mm (3′ x 6’10”) – this is the most popular for front doors
These are the door slab dimensions, not the frame or brickwork opening.
Your opening needs to be slightly larger than the door slab to allow for the frame and fitting clearances. As a rough guide, add around 10mm to both the width and the height for fitting tolerances.
If your opening doesn’t match any standard size, don’t panic. Door companies can often manufacture bespoke measurements.
Composite doors and uPVC doors are made to order anyway, so it’s not a problem if the door measurements are unique. The Advanced Group is more than certain to have a bespoke door that fits your unique household.
We will almost always carry out a survey to your home or property to ensure an accurate fit before the manufacturing process gets underway.
Common measuring for a new door mistakes
We’ve been fitting doors across Central Scotland for over 37 years, and we’ve seen every measuring mistake in the book. Here are the ones that cause the most problems.
Measuring the door instead of the door opening
As mentioned above, old doors may have been trimmed, swollen, or warped. Always measure the frame or brickwork opening.
Only measuring the door size in one place
Taking a single width measurement across the middle and calling it done is asking for trouble. Openings are rarely perfectly square, and the difference between the widest and narrowest point can easily cause a fitting problem.
Forgetting the depth
Width and height are the measurements everyone remembers.
The depth gets forgotten, and then the frame doesn’t sit flush with the wall. It’s an easy fix for a professional, but it can delay things if the right frame profile hasn’t been ordered.
Measuring in centimetres instead of millimetres
Rounding to the nearest centimetre might seem close enough, but 5mm either way makes a real difference when you’re fitting a door into an opening. In the cases of doors, millimetres matter.
Ready to replace your front door or external doors?
Once you have measured a front door, you’re in a great position to start looking at styles, colours, and finishes.
The Advanced Group is proud to be a leading supplier of composite doors and uPVC doors across Scotland, helping give your home maximum security and insulation right from opening.
Our team will always be more than happy to carry out a free home survey, where we’ll take full care and responsibility over the measurements. We can also guide you through your options and provide a free, no-obligation quote.
To learn more about our services, give our friendly team a call today to help find a new door for your home.
