How to measure windows
To measure windows for new double glazing you start with the opening: the clear size between the reveals, or between the inside edges of an existing frame or subframe. That's the size you see when you measure, but not the size you order. We make windows to their overall size, and this page shows how to get from one to the other.
Double glazing measuring tool? A tape measure will do
There's no measuring tool on our site, and you don't need one. You order on the overall size of the new frame, in millimetres, from outside edge to outside edge. That's the size you enter in the configurator and exactly the size we deliver. It's smaller than the opening, because a fitting gap has to stay free all round.
Measuring up in four steps
Measure the width at three heights: top, middle and bottom. Measure the height at two points: left and right. Take the smallest figure each time, because an opening is rarely the same size everywhere. Subtract the fitting gap your installer wants to keep, on both sides. What's left is your order size.
An example. The opening is 1,220 mm wide and 1,430 mm high at its narrowest, and your installer wants a 10 mm gap all round. Then you order 1,200 × 1,410 mm. The 10 mm is only a figure for the sum: ask whoever fits the window for the gap before you order.
Measuring uPVC windows with an outer flange
If you choose a window with an outer flange, there's a 15 to 25 mm lip on the outside that laps over the reveal or the old subframe. That lip counts in the overall size. Include it when you work back from the opening to your order size.
Measuring where there's a subframe
If the opening has a subframe, the size you read is the inside size of that subframe, and that's not your order size. Work back to the overall size and keep the gap your installer wants. We don't do that conversion for you: we don't install and don't know your joint.
Measured wrong?
We don't come out to measure, so the size you give us is your measurement. What we guarantee is the making: ±2 mm up to a metre and ±3 mm above that, with no more than 1 or 2 mm difference between the diagonals. If we're outside that, we remake the window free of charge to the size you ordered. If the size you gave doesn't match the opening, that's not covered; for that we offer a remake at cost price.
How to measure French doors and bifold doors
Doors are measured the same way: width at three heights, height left and right, the smallest figure, less the fitting gap. Pay particular attention to the floor inside and out, because that's where the threshold sits. Agree the threshold with your installer before you order.
Frequently asked questions
How do you measure windows for double glazing?
Measure the opening, not the glass: width at three heights, height at two points, the smallest figure each time, less the fitting gap. We supply complete double or triple glazed windows, frame and glass together, made to that overall size.
How do you measure for uPVC windows?
Width at three heights, height at two points, and take the smallest figure. Subtract the fitting gap and include an outer flange if you choose one. Enter the result in millimetres in the configurator; the limits of the chosen profile are shown next to the field.
How do I measure if the old window is still in?
Measure the opening as it will be, without the old window. If you can't get at it, measure the old frame on the outside and look at how it sits in the wall. If in doubt, let your installer take the size: they also know what gap they want.
Do you come out to measure?
No. We don't install and don't come out to measure, so the size you give us is the size we make. We measure every window before dispatch, and the measurement sheet comes with your order confirmation.
How do I measure the double glazing glass only?
Our windows come complete, frame and glass together, so you measure the opening, not the glass. We don't supply glass on its own; for a sealed unit in an existing frame, ask a glazier to measure it.
Know what you want? Put it together.
No form first: you watch your window take shape as you choose. The price follows in the quote, within three working days.
Configure your window or door
Where we have a guide price, it is on the page, not behind a form — not a quote and not a final price; the amount for your sizes is in the made-to-measure quote.
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