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Getting accurate measurements for replacement windows is essential for a smooth installation and proper fit. While it might seem intimidating at first, measuring windows is actually straightforward when you follow the right steps. Here’s everything you need to know to measure like a professional.
Why Accurate Measurements Matter
Precise measurements ensure you order the correct size windows from the start. Windows that are too small create gaps that are difficult to seal properly, while oversized windows simply won’t fit the opening. Taking a few extra minutes to measure carefully saves time, money, and frustration later.
Standard Measuring Convention
Always measure from the outside of your home and provide dimensions as width × height. This is the standard format used throughout the window industry, so following this convention prevents confusion when ordering.
Measuring Standard Flat Windows
Width Measurements
Take three separate width measurements to account for any irregularities in the brickwork:
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Top measurement: from the upper right corner to the upper left corner, brick to brick
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Middle measurement: at the midpoint where the window locks
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Bottom measurement: along the base of the opening
Important tip: If your home has rendering, pebble-dash, or cladding, chip away or remove enough material to expose the brick edges for accurate measurements.
Compare your three measurements and use the smallest one. Deduct 10mm from this measurement to allow for proper sealing and clearance tolerances. This gives you your final width.
Height Measurements
The process varies slightly depending on your window configuration:
Windows with a sill: Measure from the top of the existing frame (or head drip) down to the bottom of the sill. Take three measurements—left, center, and right. The manufacturer will automatically account for the sill in the total height.
Windows on concrete sills: Measure to the top of the concrete sill. Your replacement can include either a standard sill or a sub-sill depending on your preference.
Use the smallest of your three height measurements. Deduct 10mm for concrete sill installations, or just 5mm for other configurations.
Replacing Existing uPVC Windows
When replacing uPVC with new uPVC windows, you’ll also need to measure the thickness of your current glazing units. This ensures the new units fit properly into the existing frames. Remove the glazing bars (located on either the exterior or interior depending on your window type) to access the measurement points.
Measuring Bay and Bow Windows
Bay Windows
Bay windows consist of multiple flat sections joined at angles. Measure each individual section following the flat window guidelines above. The height remains consistent across all sections, but measure the width of each panel separately.
Bow Windows
Bow windows have a gentle curve rather than distinct angles. For these, you need:
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Overall width of the opening
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Height measurement
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Number of window sections
The manufacturer will calculate the individual panel sizes to create the curved effect.
Professional Measuring Recommended
For complex window configurations like bays and bows, consider having a professional surveyor take measurements before ordering. This minimizes the risk of costly errors with these more intricate installations.
Quick Measurement Checklist
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Measure from outside the home
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Take three measurements for both width and height
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Use the smallest measurement
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Record as width × height
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Deduct 10mm from width measurements
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Deduct 10mm (concrete sill) or 5mm (other) from height
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Expose brick edges if you have rendering or cladding
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For bays: measure each section separately
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For bows: measure overall width and specify number of sections
Common Measuring Mistakes to Avoid
Brickwork is rarely perfectly square, so different measurements at various points are completely normal—this isn’t a reflection of your measuring skills. The key is using the smallest measurement to ensure a proper fit.
Don’t forget to account for rendering, pebble-dash, or cladding thickness. Measuring to these surfaces rather than the actual brick will result in incorrect dimensions.
Ready to upgrade your windows with perfect measurements? Contact Expert Windows today for professional measuring services and expert window installation throughout Ireland. Our experienced team ensures precise measurements and flawless installations every time.
