How to Measure for Replacement Glass

Measuring for replacement glass takes about ten minutes per window. Get it right once and your new glass will drop straight in. Here's how.

Live in one of our free-visit cities? We offer a free measuring-up visit in selected UK cities. Pop your postcode into the quote builder to check. Everyone else, read on.

What you'll need

• A steel tape measure that reads in millimetres
• A flat-bladed putty knife or glazing tool, if you're lifting a bead
• A pen and paper, or your phone's notes app

1. Measure the glass, not the frame

We make the glass to the size of the glass. Not the frame, and not the hole you can see. The edge of the glass sits hidden inside the frame, usually 10 to 15mm on each side.

The most accurate way is to lift one glazing bead (the strip that holds the glass in) so you can see the actual edge. On most uPVC windows the beads are on the inside and push-fit out with a stiff blade. Start in the middle of a long bead and work towards the corners.

2. Width first, then height

• Measure the width at the top, middle and bottom. Write down the smallest figure.
• Measure the height on the left, middle and right. Again, write down the smallest.
• Always give width first, then height, in millimetres (900 x 1200, not 90 x 120).

Frames are rarely perfectly square, so taking the smallest reading stops the new glass binding.

3. Can't lift a bead? Measure in the frame

Measure the visible glass from bead to bead, then add how far the glass sits into the frame on each side. If you can't check that, tell us you measured the visible glass and we'll confirm with you before anything is made.

4. Measure the thickness (sealed units)

Open the window and measure across the edge of the unit, from the outside face of the glass to the inside face. Most modern uPVC windows take 24mm or 28mm units. If you get an in-between reading like 23.5mm, round up to the next whole millimetre.

5. Note the details

• Safety mark: look in the corners for a small etched stamp. That usually means toughened or laminated glass, and the replacement should match.
• Spacer colour: the strip around the edge between the two panes (silver, white, black and so on).
• Pattern: if it's obscure glass, a photo helps us match it. Some patterns run one way, so double-check width and height.
• Bars: any Georgian bars inside the unit, and how many each way.

When you need safety glass

Building Regulations call for safety glass (toughened or laminated) in certain places, including doors, panes next to doors and low-level glazing near the floor. Bathrooms near a bath or shower are another common one. Rules vary across England, Wales, Scotland and Northern Ireland. If you're not sure, choose "Not sure" in the quote builder and we'll advise. This is a general guide, not legal advice.

Check twice, order once

Every pane is made to your measurements, so it can't be resold if a size is wrong. Measure each window twice, write the sizes down straight away, and label them by room (for example "Kitchen left") so nothing gets mixed up.

Ready?

Start your quote. Add as many panes as you need and send them in one go. Rough sizes are fine to begin with, and we'll check the details with you before anything is made.