Measuring for a new window

Measure with, height and diagonal for your new window.

Measuring for a new replacement window is not difficult, and you should have no problems, provided you take care and proceed in an orderly way. However, if you don't get the correct measurement, you could end up with a window that doesn't fit, which is embarrassing and expensive.

Before you start, getting a tape measure, notebook and spirit level is a good idea. The latter is optional but can help ensure your measurements are as accurate as possible. The best way to measure a new window is outside the property. You can measure from the inside (probably the best option for windows above the ground floor), but the outside measurements will be more accurate.

If you have your window fitted by a professional installer like Select Window Systems, they will take care of all the measurements for you, so you can be confident they will get it right. You can measure yourself to get a rough quote guide, but the installer will also make their own measurements.

If you are ordering your frame directly from the manufacturer, use the instructions here as a guide. Although most manufacturers use metric millimetres for windows, checking first is always worthwhile.

Do not make the common mistake of getting your measurements from the old window frame. There is a decent chance the old window could have been poorly fitted in the first place and gaps and holes are filled with padding and caulking to make it fit. The area to measure is the hole left when the old window has been removed and all the extra padding, rendering and insulation removed.

Measure the window width

First, measure the width of the window hole from brick to brick. Keep the tape taut and horizontal (this is where a spirit level can help), and take three measurements at the window's top, middle and bottom. Ideally, all three measurements will be the same; if not, take the smallest of the three. Then, you can be sure the window will fit widthways, even if gaps exist.

Measure the window height

Next, measure the height, following the same procedure and measure from the window sill at the bottom to the lintel at the top again making three measurements, this time to the left, centre and right of the window. Keep the tape taut and upright for accuracy, and note the shortest of the three lengths.

Check the window is square

Now, it's time to check that the hole is square. Measure from the top left corner to the bottom right and again from the top right to the bottom left. If they are both the same, the window opening will be square.

If not, the opening will be 'racked', and adjustments will be required when the window is installed. This often happens in older buildings where openings have been skewed by subsidence or other movement. With the shortest measurements recorded for width and height, this should not be a problem for the installer, but some extra installation work may be needed.

More measurements needed

When replacing an existing window, you must also check the depth of the frame from inside to outside to ensure a perfect fit for your new frame. Some window manufacturers prefer that you deduct between 5mm and 10mm from brick-to-brick measurements to ensure the window has room to settle once installed.

If the fit is too tight, there may not be room to apply sealant around the frame. If the fit is too loose, gaps between the wall and frame may be left, affecting the window's overall thermal efficiency.

Double check everything

It's a good idea to take all the measurements twice. This may sound like overkill, but it's far easier to correct a mistaken measurement than an ill-fitting window when it arrives on site. Please note that this advice is for guidance only. Check first with your supplier or installer on their specific measuring requirements.

Use the professionals

Select Window Systems knows that accurate window measurement is crucial for ensuring your new window's perfect fit and optimal performance. Skilled professionals and account for any irregularities in the structure.to provide a tailored solution so new windows look great and perform efficiently.

Our team is dedicated to making the window measurement and installation process seamless. Contact us today to schedule your consultation and discover how we can transform your property with beautiful, energy-efficient replacement windows.