How To Guides — UPVC Windows

Watch our step-by-step video guides covering everything from measuring to installation.

Guide 1

How to Measure Your Windows

Measure windows from the outside using the brickwork opening, in millimetres (mm). Measure the width in three places (top, middle, bottom) and the height in a few places, then use the smallest measurements and deduct about 10mm. Exclude any metal lintel from the height, and if the window sits on a cill, measure from underneath it unless the cill is fixed (such as stone).

How To Guides — UPVC Windows

Watch our step-by-step video guides covering everything from measuring to installation.

Guide 1

How to Measure Your Windows

How To Guides — French Doors

Watch our step-by-step video guides covering everything from measuring to installation.

Guide 1

How To Measure Your Doors

Measure French doors from the outside brickwork opening in millimetres (mm). Measure the width in three places (top, middle, and bottom) and the height in several places, then use the smallest measurements and deduct about 10mm. Always measure the height down to the finished floor level, not the subfloor or existing threshold.

How To Guides — Composite Doors

Watch our step-by-step video guides covering everything from measuring to installation.

Guide 1

How To Measure Your Doors

Measure composite doors from the outside brickwork opening in millimetres (mm). Measure the width in three places (top, middle, and bottom) and the height in several places, then use the smallest measurements and deduct about 10mm. Always measure the height down to the finished floor level, not the subfloor or existing threshold.

How To Guides — Roof Lanterns

No guides added yet.

Guide to Measuring Your UPVC Windows

Follow these simple steps to measure your windows accurately. All measurements should be taken in millimetres (mm) from the brickwork opening on the outside of your property.

Step 1

Windows are measured from the external brickwork opening of your property, always in millimetres (mm).

Start by measuring the width from brick to brick in three places: top, middle, and bottom. Take the smallest measurement and deduct 10mm to get your final width.

Step 2

Measure the height of the opening in a few different places and take the smallest measurement. Deduct 10mm to get your final height.

If there’s a metal lintel, exclude this from your measurement. Most windows sit on a cill — where possible, measure from underneath the existing cill, unless it can’t be removed (e.g. stone).

Please note: If your property is rendered then it's a good idea to remove some of the render in order to view the brickwork edge. Depending on the thickness of your render you may require frame extenders.

Important Points to Remember

Some important points to remember Measure from outside, brickwork to brickwork. If that is not possible, measure your existing window. Provide us with the overall window sizes including cills or extenders/add-ons (except stone cills or if you're ordering windows without cills). Measure in a few different positions, take your smallest size and deduct approximately 10mm. If in doubt, just ask! If you need any further help, why not take a few photos and email them to us for specific advice.

Guide to Measuring Your UPVC Windows

Follow these simple steps to measure your windows accurately. All measurements should be taken in millimetres (mm) from the brickwork opening on the outside of your property.

Step 1

Windows are measured from the external brickwork opening of your property, always in millimetres (mm).

Start by measuring the width from brick to brick in three places: top, middle, and bottom. Take the smallest measurement and deduct 10mm to get your final width.

Step 2

Measure the height of the opening in a few different places and take the smallest measurement. Deduct 10mm to get your final height.

If there’s a metal lintel, exclude this from your measurement. Most windows sit on a cill — where possible, measure from underneath the existing cill, unless it can’t be removed (e.g. stone).

Important Points to Remember

Some important points to remember Measure from outside, brickwork to brickwork. If that is not possible, measure your existing window. Provide us with the overall window sizes including cills or extenders/add-ons (except stone cills or if you're ordering windows without cills). Measure in a few different positions, take your smallest size and deduct approximately 10mm. If in doubt, just ask! If you need any further help, why not take a few photos and email them to us for specific advice.

Guide to Measuring Your French Doors

Get precise measurements for your French doors with this step-by-step guide. All measurements should be in millimetres (mm).

Step 1

French doors are measured from the external brickwork opening, always in millimetres (mm).

Measure the width from brick to brick in three places, top, middle, and bottom. Take the smallest measurement and deduct 10mm to allow for fitting.

Step 2

Measure the height of the opening in a few different places and take the smallest measurement. Deduct 10mm to get your final height.

Always measure down to the finished floor level, not the subfloor or existing threshold. If there’s an existing cill or step, measure from the top of the finished floor surface.

If your property is rendered, remove some render to view the brickwork edge before measuring. Depending on render thickness you may require frame extenders.

Important Points to Remember

Important points to remember Measure from outside, brickwork to brickwork. If that is not possible, measure your existing door frame. Always measure to finished floor level — French doors are supplied to sit flush with your finished floor surface. Measure in a few different positions, take your smallest size and deduct approximately 10mm. Note whether your opening has a step or existing threshold — this affects how the cill or weather bar is specified. If in doubt, take a few photos and email them to us for specific advice.

Guide to Measuring Your Composite Door

Accurate measurements ensure your composite door fits perfectly first time. Measure in millimetres (mm) from the structural brickwork opening.

No Measuring Needed

All of our composite doors are supplied as complete units, designed to fit standard UK door openings, but it’s still important to take accurate measurements before ordering.

Step 1

Measure the width of your door opening from brick to brick in three places: top, middle, and bottom. Take the smallest measurement and deduct 10mm to get your final width.

Step 2

Measure the height of the opening in a few different places and again use the smallest measurement. Deduct 10mm to get your final height.

Step 3

Measure from the top of the opening down to the finished floor level. If there’s an existing cill, measure from the top of the cill unless it’s being removed or replaced.

Step 4

If your property has any uneven brickwork, render, or obstructions, make sure these are accounted for - your measurements should reflect the true usable opening.

We are unable to accept responsibility for doors ordered for non-standard frames. If in doubt, please check with us before ordering.

Important Points to Remember

Before ordering, confirm that your existing frame is a standard UK size. If you're replacing an older door, most UK homes use a standard frame — but it's worth a quick check. If you're unsure, take a photo of your current door and frame and email it to us — we'll confirm compatibility before you order.
Important points to remember No measuring required — all our composite doors are one standard size and fit a standard UK door frame. Check that your existing frame is a standard UK size before ordering — this is the only thing you need to confirm. All doors are supplied as a complete ready-to-fit unit — just choose your style, colour, glazing and hardware. If you're replacing an existing composite or timber door, the swap is usually straightforward — your installer will confirm on survey. Not sure if your frame is standard? Take a photo and email it to us — we'll check before you order.

Guide to Measuring Your Roof Lantern

Measure your roof opening carefully using this guide. All measurements should be taken in millimetres (mm).

Step 1

Roof lanterns are measured from the structural opening (the aperture), not the outer edge of the upstand or kerb.

Measure the width of the opening in a few different places and take the smallest measurement. Deduct 10mm to allow for fitting. Always measure the clear structural opening, excluding any upstand or timber frame.

Step 2

Measure the length of the opening in the same way - multiple positions, take the smallest measurement, then deduct 10mm.

Also check the height of your upstand (the kerb the lantern sits on). A minimum of 150mm is recommended, if yours is lower, let us know and we can advise.

We supply roof lanterns to fit the aperture opening. If your upstand is not yet built, we recommend constructing it first and then measuring — small variations in a new build can affect the fit.

Important Points to Remember

Important points to remember Always measure the aperture opening — the hole in the roof — not the top of the upstand or the outer footprint. You need two dimensions: width and length. Measure each in multiple positions and use the smallest figure. Also measure and note your upstand height. A minimum of 150mm is recommended for correct weatherproofing. Check that your upstand is square and level before ordering — an out-of-square kerb will affect the seal and fit of the lantern. If in doubt, take a few photos and email them to us for specific advice.

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5.0

Based on 30 reviews

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1-5 of 30 reviews

Mia
Reviewer

March 31, 2026

Roof Lanterns
Five stars all the way! This product is worth every penny. It's user-friendly and has improved my productivity significantly.
Andrew
Reviewer

March 31, 2026

Flush Windows
Impressive product! It delivers on its promises and has made a positive impact on my daily routine. Very satisfied with the purchase.
Harper
Reviewer

March 31, 2026

Standard Windows
Excellent purchase! The product lives up to the hype, and I couldn't be happier with the results. Definitely worth considering.
Mia
Reviewer

March 31, 2026

Composite Doors
Outstanding! I can't fault this product in any way. It does exactly what it's supposed to do, and I'm extremely happy with it.
David
Reviewer

March 31, 2026

French Doors
Five stars all the way! This product is worth every penny. It's user-friendly and has improved my productivity significantly.