• May 25, 2024

How to Measure the Size of Replacement Windows

Replacing your windows can be daunting. Not only do you need to determine the size of the window you need, but you also need to ensure that the replacement window will fit perfectly in the existing opening. To ensure a perfect fit, you need to measure the size of the window accurately. Only then the replacement window company will be able to give you a correct estimate. Here are some tips to help you measure the size of replacement windows correctly.

Measure the Width of Your Window

Now, the width of the replacement windows is very important. After all, the width of the replacement window will determine the number of the glass panes. When you are buying a replacement window then you need to check the available space for the windows.

If the available space is big enough then you can go for the double-hung windows. Double hung windows are the most popular types of replacement windows. You can replace the windows of your house with double-hung windows.

To measure your replacement window size, you’ll need to first measure the glass width on each side of the window frame. To do this, use a tape measure and make sure it’s pulled tight against the frame.

Next, measure the width of each mullion (the horizontal piece between two vertical pieces) as well as that of each vertical piece itself.

Finally, take a look at how wide your current windows are and record their measurements so that you can compare them later on when you’re considering sizing options for new ones!

Measure the Height of Your Window

The height of your window is important. The height of the replacement windows will depend upon the design and style of the house. 

Most of the times people choose the windows that are taller than the existing windows. But if you are replacing the windows then you need to consider the height of the window first.

If you are replacing the windows then you need to calculate the height of the window, by measuring the height of the walls of the room and then the height of the window frame. The height of the window frame will help you to choose the correct size of the window.

The top of your replacement window should be at least 1 inch shorter than the bottom of your existing frame. 

This creates airflow that prevents water damage and helps keep air moving through your home, which can help lower heating and cooling costs.

So how do you measure it? Use a tape measure:

  • Measure from the top inside corner of one window frame to the other inside corner (highest part).
  • Add 2 inches to this number (this accounts for any trim around your existing windows).
  • Measure the Depth of Your Window. This is the measurement from the outside frame of the window to its center.



Now that you’ve learned how to measure the size of replacement windows, you’re ready to make your purchase. But if you want a quick cheat sheet for reference, let’s go through it one more time:

  • Take a tape measure and measure the width and height of your current windows, including any trim. 
  • Make sure also to include any glass that extends beyond these measurements, such as an inset pane or decorative glass pattern.
  • To get accurate measurements for new replacement windows, hold a measuring tape at eye level against all four sides of your current window.
  • Mark each end with a pen or pencil (a pencil can be wiped off if you make an error). Then use those marks when measuring for new replacement windows so that everything will line up properly once installed.
  • Measure the width of your current frame opening and subtract 3/4″ from this measurement (the 3/4″ is used to account for the nailing flange).
  • Use an outside-edge measurement as well. This is especially important if you’re trying to compare sizes between two different window manufacturers’ products because they may not use the same measurements.


In conclusion, measuring replacement windows is not as complicated as it may seem. With the right tools, the right preparation and knowledge, you can easily determine the right size of window that needs to be replaced. Do not forget to add an extra quarter-inch to your measurements. Then, the window will fit perfectly and securely into the openings. Always be sure to double-check your measurements. Select a window that has a proper seal to ensure that your home remains energy efficient.

James William

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