How to Measure Your Window for a Custom Aluminum Replacement

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To measure a window for replacement, record the width and height of the opening at three points each and use the smallest figure, then check the depth and whether the frame is square. Take all measurements in millimeters, note any obstructions, and send them with photos so the factory can draw an accurate specification.

Why Accurate Measurements Matter

A custom aluminum window is made to the exact size of your opening, so small errors cause real problems later. If the frame is too big it will not fit, and if it is too small you will have gaps that let in water, air and noise. Taking careful measurements before you order saves time, avoids rework and keeps the installation on schedule.

Measure the opening itself, not the old window frame, because the old frame may have been installed with gaps or may have shifted over the years. Work slowly, write everything down, and measure twice before you send any numbers to the factory.

Tools You Will Need

You do not need professional equipment, but a few simple tools will make the job reliable:

A steel measuring tape, preferably 5 meters long
A spirit level or a long straight edge
A pencil and notebook, or a phone for photos
A helper to hold the tape at the far end

Use a steel tape rather than a flexible cloth one, since fabric can stretch and give inaccurate readings.

Measuring Width and Height

Measure the width of the opening at the top, middle and bottom, and record each reading. Then do the same for the height at the left, center and right. Walls are rarely perfectly straight, so these three readings show you whether the opening varies.

When ordering, use the smallest width and the smallest height you found. This ensures the new window will fit even at the tightest point, and any small difference can be handled with the installation sealing. Write down the figures in millimeters, and label which one is width and which is height.

Checking Depth and Reveal

Depth is the distance from the face of the wall to the back of the opening, where the new frame will sit. Measure it at a few points, since the reveal can differ from one side to the other. Depth tells the factory how deep the frame must be and whether a sill or extra trim will be needed.

Also check for any obstacles such as shutter boxes, pipes, electrical boxes, or a protruding ledge. Mark them on your sketch, because they can affect how the new window is positioned and fixed.

Checking Square and Level

An opening is rarely perfectly square. Measure both diagonals from corner to corner. If the two diagonal readings differ noticeably, the opening is out of square, and the factory will need to allow for it when drawing the window.

Use your spirit level to check whether the top and bottom of the opening are horizontal and whether the sides are vertical. Note any slope or lean. These checks are normal for older buildings and are easy to plan for when you share them early.

Sending Your Measurements and Photos

Once you have your figures, prepare a simple inquiry. Include the three width and three height readings, the depth, both diagonals, and a clear photo of the opening taken straight on, plus one from the side showing the depth. Add a short note about the window type you want, whether it is for a balcony or a room, and which direction it faces if you know it.

Our team reviews this information and, where needed, arranges an on-site measurement before drawing the final specification. You then approve the drawing and written details before production begins in our factory.

Frequently asked questions

Should I measure the old window frame or the opening?

Measure the opening in the wall, not the old frame. The frame may have been installed with gaps or may have moved, so the opening gives the true size for the new window.

Which measurement should I give for width and height?

Give the smallest width and smallest height you recorded at the three points. This makes sure the new window fits even at the tightest spot.

What if my diagonal measurements are different?

A difference between the two diagonals means the opening is out of square. Tell the factory about it so the window can be drawn to suit the actual shape of the opening.

Do I need to measure in millimeters?

Yes, please record all measurements in millimeters. Consistent units avoid confusion and help the factory produce a precise drawing.

Common mistakes to avoid

The most common errors are measuring only once, using the old frame instead of the opening, and forgetting to note obstacles or out-of-square corners. Always double-check and send photos with your figures.

Our recommendation

Take at least two sets of measurements on different days and compare them, and have a second person check the tape reading. If you are unsure about anything, send photos and let the team arrange an on-site measurement.

Summary

Measure the opening at three points for width and height, check depth and both diagonals, note obstacles, and send millimeter figures with clear photos to get an accurate custom aluminum window.

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