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How to measure for replacement windows

October 04, 2022

Gabled homes with stone brick and glass window on walls against cloudy blue skyIf you’re replacing your windows, you might be wondering how to measure the opening to ensure the new ones will fit properly. Mismeasuring the window opening can create massive headaches as you have to re-measure and reorder the windows in the correct size—meaning it will add an additional expense and take longer to replace your old windows with beautiful new ones. To make the process as smooth as possible, ensure you write down each window measurement precisely and follow some of the guidelines below to get it right the first time.

Check for Square

Make sure that the opening is actually at a 90-degree angle. If the window opening is not at a 90-degree angle, the replacement window will not fit properly, and it’s likely that you won’t be able to operate it. Measure the window diagonally from top right to bottom left and then top left to bottom right. If the difference between these measurements is more than ¼”, you should choose a new-construction window to accommodate the shape of the opening instead of a replacement window.

Measure Each Part of The Opening

To get the most accurate numbers, use the following methods to measure your window opening. Be sure to record every measurement as you go.


Measure the height from the top horizontal jamb to the bottom windowsill (the sill is the piece on which the window sash rests when the window is closed). You will need a measurement for the window’s far right, far left, and middle sections.


First, measure the top from jamb to jamb with the window closed. Then, measure the bottom from jamb to jamb at the lowest point. Finally, to measure the middle, keep the window open and measure across the middle from jamb to jamb as well.


It’s important to check that your window opening is deep enough to accommodate a replacement window. Measure the sill from front to back and check that it is at least 3 ¼” deep.

After you have all these measurements, round down to the nearest eighth of an inch. The experts at Five Star Improvements will be able to help you order windows that fit your home perfectly.

Contact Our Team

If you need more assistance measuring the opening for your new replacement window or want to partner with experts in window installation, reach out to Five Star Improvements. We can help with all types of home improvement projects, and we can ensure your new windows are high quality and correctly sized. Contact us today!

Extending Unparalleled Service & The Ultimate Home Improvement Experience

Remodeling your home can be a long, stressful, and exhausting process. But, it doesn’t have to be. Simply partner with Five Star Improvements. We put our customers above all else, making sure that they are comfortable and content throughout the home improvement process. We strive for 100% customer satisfaction, and we always go the extra mile to ensure just that. And, if anything goes awry at any point during the project, then we will not stop until we rectify the problem.

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