Measuring Windows for Security Bars: A Contractor's Guide

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Measure the window opening at several points for width and height, check the frame depth, and note the mounting surface and any obstacles such as shutters or handles. Take photos and sketch the layout so the fabricator can produce bars that fit the opening on the first attempt.

Why Accurate Site Measurements Matter

Security bars are made to measure, so every millimeter counts. A bar that is even slightly too large will not fit the opening, and one that is too small will leave gaps that defeat its purpose. Walls and window frames are rarely perfectly square, especially in older buildings, so a single measurement is never enough.

Good measurements save time on both sides. The factory can prepare drawings and production with confidence, and the installer avoids repeat visits and rework on site.

Tools You Need on Site

Bring a steel tape measure, a long straightedge or level, a pencil, a notepad and a camera or phone for photos. A small square helps check corners, and a flashlight is useful for looking inside recesses and behind frames.

Steel tape for width and height
Level or straightedge for plumb and square
Camera for every opening, from front and angle
Sketch paper for quick layout drawings

Measuring Width and Height Correctly

Measure the width at the top, middle and bottom of the opening, and the height at the left, centre and right. Record the smallest value in each direction, since that is the limit the bar must fit within. Measure from the inside face of the frame or reveal where the bar will sit, not from the outer wall line.

Write every dimension on your sketch with its location, such as top width or left height, so nothing is confused later.

Checking Depth, Frame Type and Mounting Surface

Depth determines how the bar is fixed. Check whether the frame is aluminum, steel or masonry, and whether there is enough solid material for anchors or welded connections. Note the thickness of the reveal and whether the wall is brick, concrete or cladding.

Look for loose plaster, cracks, moisture or damaged frames. These conditions need to be recorded and sometimes repaired before installation can take place.

Noting Obstacles and Opening Operation

Before you finish, check how the window opens and what could interfere with the bar. Handles, hinges, stay arms, shutter boxes, air-conditioning pipes and electrical boxes all affect placement. Test that the window can still open fully once the bar is in position.

Opening type: sliding, casement or tilt
Handle and hinge positions
Shutters, blinds or screens
Pipes, cables and wall fixtures

Preparing the Drawing and Handover to the Factory

Combine your measurements, photos and sketch into a single clear document. Mark the orientation of each window, the floor and room, and the inside and outside faces. Include notes on finish preferences, such as galvanizing or powder coating, if the client has already chosen one.

Send the file to the factory with the client's name and address before production begins. The team can then review the specification and confirm any points that need clarification, which is far cheaper than fixing a wrong dimension later.

Frequently asked questions

How many measurements should I take for each window?

Take at least three width measurements and three height measurements, at different points across the opening. Use the smallest figures recorded, since the bar must fit within the tightest point.

Should I measure from the frame or from the wall?

Measure the clear opening inside the frame or reveal where the bar will sit. Measurements taken from the outer wall line will not reflect the space available for the bar.

What if the opening is not square?

Record both diagonals and note the difference between them. The fabricator can then account for the out-of-square condition in the drawing so the bar fits the actual opening.

Do I need to measure before or after the plaster is finished?

Measure after the final plaster, tiling or cladding is in place. Measurements taken before finishing work may change and lead to a bar that does not fit.

Common mistakes to avoid

The most common error is measuring only once and from the outer wall rather than the clear opening. Skipping the check for handles, shutters and obstructions also leads to bars that do not allow the window to open properly.

Our recommendation

Measure twice, record the smallest dimension in each direction, and photograph every opening with a reference sketch before leaving site. A clear, labelled set of measurements is the best way to get bars that fit on the first installation.

Summary

Accurate site measurement of width, height, depth, mounting conditions and obstacles is the foundation of a well-fitting security bar. Clear notes and photos make the handover to the factory smooth and reduce costly corrections.

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