What Size Window Seal Do I Need? Wedge, Bubble & Flipper Gaskets Explained

The rubber strip around the glass and around the edge of the opening window is called a gasket. You'll also see it called a window seal, a rubber seal or a weatherseal. They all mean the same thing. When it goes hard, shrinks or comes away, you get draughts, rattles and rain getting in around the frame.

"What size seal do I need?" is one of the most common questions we get. Here's how to work out which one you've got, based on what our customers actually buy.

Got a piece of the old seal in your hand? Jump to how to match it, or see the Gasket Finder with a photo of every seal we sell.

Which seal are you replacing?

A uPVC window or door usually has more than one seal. Check which one has failed before you order:

• The seal around the glass, between the glass and the frame. This is usually a wedge gasket, pushed in beside the glass.
• The seal the opening window or door closes against. This is usually a bubble gasket or a flipper gasket.
• Misting or condensation between the two panes of glass. That isn't the gasket. The sealed glass unit itself has failed, and a new seal won't fix it.
• A draught or rain under the front door. That's usually the bottom of the door, not the gasket. See how to stop rain coming in under your front door.

Window seal types: what we actually sell

The single most popular seal is the R3233G wedge gasket, at about 3,300 metres in a year. The most popular bubble seal is the R6160, at about 2,350 metres. We sell 9 sizes of wedge, 6 of bubble and 1 flipper, so even the best seller is only about 1 in 8 metres of the seal we sell. That's why matching your old seal matters more than picking the popular one.

We also sold about 6,200 metres of Schlegel Qlon foam weatherseal, almost all of it to the trade at our counter, and over 1,800 gasket sample packs.

Why isn't there a standard window seal size?

uPVC windows and doors are made from dozens of different frame systems, by different manufacturers, over several decades. Each system has its own groove shape and its own gap between the glass, the frame and the opening part. The seal has to fill that exact gap:

• Too small, and it won't seal, so you still get draughts and rattles.
• Too big, and it won't push into the groove, or the window becomes hard to close.

Two seals can look almost the same and still be a different size. That's why every seal has a code, and why we sell sample packs.

Wedge, bubble or flipper: how to tell them apart

Each seal's product photo shows its profile, so you can compare it with the end of your old piece. The Gasket Finder puts them all on one page.

Bubble and flipper seal sizes

These are the sizes of every bubble and flipper seal we sell, from our bubble sample pack card. All sizes are in millimetres. The height is the bulb or flipper standing above the frame, and the foot is the part that pushes into the groove.

Three bubble seals are 5.5mm high, so check the foot width and the shape as well. For wedge seals, match your old piece against the wedge sample pack.

How do I find my exact window seal size?

1. Pull out a short piece of the old seal, about 5–10cm. Start at a corner, where it's easiest to lift. Most seals pull straight out of their groove.
2. Look at the end of the piece to see its shape: solid wedge, hollow bubble or thin flipper. For a bubble or flipper seal, measure its height and the width of its foot with a ruler and check them against the size table.
3. Compare it with the photos on the Gasket Finder, or hold it against each piece in a sample pack until you find the one that matches in shape and size.
4. Check the fit. Push the matching sample into the groove. It should go in firmly and stand up the same as your old seal.
5. Note the code, such as R3233G, and order that seal by the metre.

Don't go by an old seal that has squashed flat or shrunk. It will look smaller than it really is. Compare the foot, the part that sits in the groove, because it's less likely to have worn.

Not sure which one you've got?

The wedge sample pack has a piece of every wedge seal we sell, about 10cm each, labelled with its code. £0.99.

View the sample pack →

How much window seal do I need?

• A standard uPVC door needs about 6 metres.
• A window: measure all the way round the frame where the seal sits, and add the sides of the opening part if that seal needs replacing too.
• Round up to the next full metre. Our seal is sold by the metre and sent as one continuous length.

Because it's cut to the length you order, cut seal can't be returned. That's one more reason to match it before you buy.

See every seal in door and window seals and gaskets.

How do I fit a new window seal?

1. Pull the old seal out of its groove all the way round.
2. Clean the groove with a dry cloth or a vacuum, so there's no dirt or old rubber left in it.
3. Start at a corner and push the new seal's foot into the groove with your thumb, working along the frame. Don't stretch it as you go, or it will shrink back and leave gaps.
4. Go round the corners in one length where you can, and cut the end square so the two ends meet tightly.
5. Close the window or door and check it shuts properly and the seal touches all the way round.

If it won't go in, it's probably the wrong size. Stop and check it against your old piece rather than forcing it.

Don't want to match it yourself?

• Send us a photo of the end of your old seal next to a ruler, and we'll tell you the code.
• Bring a piece in to our Aintree trade counter and we'll match it.
• Use the Gasket Finder to compare it with a photo of every seal we sell.

More "what's the standard size?" guides

• Door locks (euro cylinders): 35/35 is the most common, but 2 in 3 doors need another size.
• Window handles: espag screw centres are almost always 43mm, but spindle lengths vary.
• uPVC door handles: 82% are 92mm PZ, but the screw centres vary.
• Letterboxes: 10 inch or 12 inch, split almost evenly.