How to Measure Window (for Replacement)
The most accurate way to measure window is on the outside of the building. When measuring window, take three readings for the width and height. One from the centre, and to each side. Never measure the old frame.

The task of measuring a window for replacement is simple. On the other hand, issues arise if your measurements are incorrect.
If you are even a few centimeters off on your measurements, your replacement frames might not fit.
If you know of someone changing windows, you should insist that the installer accept responsibility for measuring so they may be held accountable for any problems.
Before moving forward, make sure you discuss and get confirmation that the windows will be measured by a respected manufacturer and installer. We at Safe and Sound Windows are in charge of all window measures, so if something goes wrong, we fix it.
To obtain an approximate quotation, measure window and refer to the guidelines provided below. However, ensure that the installation takes new measurements.
Those who wish to purchase frames straight from a manufacturer can refer to the guidelines provided below.
First, find out whether your manufacturer has any special requirements by contacting them. While the majority of manufacturers measure window in the same way, others do not
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Preparing for Window Measurement
Before diving into the measurement process, it’s essential to gather the necessary tools and ensure proper preparation. Here’s what you’ll need:
Tools Required
- A sturdy tape measure (preferably a retractable metal one)
- A notepad and pen (or a digital device for recording measurements)
- A level (optional, but recommended for checking if the window opening is square)
- A ladder or step stool (if measuring exterior windows from the outside)
Preparation Steps
Clear the Area: Remove any obstructions around the window, such as curtains, blinds, or furniture, to ensure unhindered access to the window frame and opening.
Clean the Window Frame: Gently wipe down the window frame to remove any dirt or debris that could interfere with accurate measurements.
Decide on Measurement Location: Determine whether you will measure from the interior or exterior of the home. While interior measurements are more convenient, exterior measurements are generally more accurate and recommended by most professionals.
Measuring Window Openings: Step-by-Step Guide
Once you’ve prepared the area and gathered the necessary tools, it’s time to start measuring. Follow these step-by-step instructions to ensure accurate measurements:
Step 1: Measure the Width
Locate the window opening’s left and right edges, ensuring you measure from the rough opening (the structural opening in the wall) rather than the existing window frame.
Take three width measurements: one at the top, one at the center, and one at the bottom of the opening.
Record the smallest of the three measurements as the final width measurement.
Step 2: Measure the Height
Locate the window opening’s top and bottom edges, again measuring from the rough opening rather than the existing frame.
Take three height measurements: one on the left side, one in the center, and one on the right side of the opening.
Record the smallest of the three measurements as the final height measurement.
Step 3: Check for Square
To ensure a proper fit, it’s essential to check if the window opening is square. Follow these steps:
Measure the diagonal distance from the top left corner to the bottom right corner of the opening.
Repeat the measurement from the top right corner to the bottom left corner.
If the two diagonal measurements are identical, the opening is square. If not, make a note of the discrepancy, as it may require additional considerations during installation.
Step 4: Account for Deductions (if applicable)
Some window manufacturers recommend deducting a small amount (typically 1/4 inch or 6.35 mm) from the rough opening measurements to allow for proper installation and accommodation of potential shifts or settling in the building structure.
Check with your manufacturer for their specific recommendations and adjust your measurements accordingly.

Confirming Measurements with the Installer
Even after taking accurate measurements, it’s always recommended to have the professional installer confirm the measurements before ordering the replacement windows. This helps ensure that any potential discrepancies or special considerations are addressed, preventing costly mistakes.
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