How to Measure Aluminum Windows Correctly Before Ordering

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To measure aluminum windows, record the width and height of the opening at three points each, use the smallest figure, and note the wall depth and any obstructions. Take the measurements to the exact opening rather than the old frame, and confirm them on site with a professional before production starts.

Why accurate measurement matters

A window is made to measure, so the figures you give decide how well it fits. A few millimeters of error can mean a frame that won't sit square, a gap that lets in water and noise, or a unit that has to be remade. Good measurements save time, reduce waste and make installation smoother for everyone involved.

Before you start, be clear about what you are replacing. Measure the actual opening in the wall, because the old frame may have been installed unevenly or may hide damage.

Tools you need for measuring

You do not need specialist equipment, but a few tools make the job more reliable:

A steel tape measure, preferably 5 meters or longer
A spirit level or long straight edge
A notepad and a pencil, plus your phone for photos
A ruler or caliper for small depth readings

Use one tape for the whole job so you are not mixing readings from different instruments.

Step-by-step: measuring width and height

Measure the width at the top, middle and bottom of the opening, and the height at the left, center and right. Record all three readings for each dimension. Use the smallest width and the smallest height, since the window must fit inside the narrowest point.

Measure from inside edge to inside edge of the reveal
Check corners for diagonal difference, which shows whether the opening is square
Write each reading down immediately rather than relying on memory

Measuring depth, sills and obstructions

Depth tells the maker how deep the frame can sit and whether a sill or extra profile is needed. Measure the wall thickness at the reveal and note the surface finish, such as plaster, stone or tile, since finishes add thickness.

Also record anything that affects the installation: shutter boxes, roller housings, ledges, pipes, electrical boxes and the position of the handle side. Photos with a tape held along the measured line are very helpful.

From measurement to drawing and approval

Once measurements are taken, the factory can prepare a drawing and a written specification. This document should show the overall size, the opening type, the glazing, the frame profile and the color or finish. Read it carefully before approving.

Check that the drawing matches the room: confirm which side opens, where the handle sits and whether the window is fixed or operable. Approve only when every detail is correct, because changes after production are costly.

Production, finishing and installation

After approval, the window is produced in the factory with cut, welded and assembled aluminum profiles. Finishing is applied to protect the surface and match your design, and the unit is checked before it leaves the workshop.

Installation should be done by a qualified team that levels the frame, seals it correctly and tests opening and locking. A good fit at this stage protects the window from water, drafts and early wear.

Frequently asked questions

Should I measure the old window frame or the opening?

Measure the opening in the wall, since the old frame may be damaged, uneven or undersized. The new window must fit the actual space, not the previous unit.

What if the opening is not square?

Compare the two diagonals; if they differ, the opening is out of square. Tell the maker, who can account for this in the frame design and installation plan.

Do I need to measure again after plastering or tiling?

Yes, if the finish will change the reveal size or depth. Measure after the wall work is complete so the window matches the final dimensions.

Can I order from my own measurements alone?

You can, but an on-site measurement by the manufacturer or installer is recommended. It catches hidden issues and reduces the risk of errors before production.

Common mistakes to avoid

The most common error is measuring only once or using the old frame instead of the real opening. Skipping photos and notes also leads to disputes when the window arrives.

Our recommendation

Take three readings for width and height, write everything down, and have the maker confirm the measurements on site before production. This single step prevents most fitting problems.

Summary

Measure the opening at several points, use the smallest figures, record depth and obstructions, and confirm the drawing before approving production.

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