How to Measure Your Windows in 3 Steps

One of the biggest reasons homeowners would need to know how to measure windows they already have is to get ready for replacement windows. Other reasons homeowners might also measure their windows if they're thinking about getting custom blinds or if they want to make adjustments to their home that require structural changes. 

If you're looking to replace your windows, an important step in getting great new glass is measuring your windows correctly. We’ll go over everything you need to know about how to measure for replacement windows to get the most accurate information.

Learning more about replacement windows helps you have confidence when you measure for replacement windows at your home. Then you can purchase new windows with peace of mind.

Measuring window sizes in 3 steps

The good news is that understanding how to measure windows isn't complicated. By following some easy steps, you can get the measurements you need to ensure great-fitting replacement windows.

1. Measuring the width of windows

First, you want to find out how wide your windows are. When measuring the width of windows, you'll take three horizontal measurements. Measure from side to side at the top, middle, and bottom of your window. Then circle the smallest of the measurement. This is the number you use for the rough opening. 

When ordering windows, you always go by the width first, then the height. Taking the measurements this way reduces any chances of making a mistake when ordering.

2. Measuring the height of windows

After you know the width, measure the height of the window. Take this measurement the same way, by measuring in three places and choosing the smallest figure. One measurement should be in the middle, with the other two on the left and right sides. 

Some window sills are sloped. If you have sloped sills, you want to take your window measurement right against the window. That's generally the highest point.

When you're focusing on how to measure for replacement windows, you also want to know the depth of the window opening. Measure from the outside edge to the inside edge of the window frame in several places. Again, choose the smallest measurement.

For windows that don't open, you can measure the outside and inside depth and add them together, along with the thickness of the window itself.

3. Measuring the rough opening for replacement windows

A rough opening for a window is the full opening that the window fits inside. It's typically two inches larger than the actual window to allow for adjustments and leveling when the window is installed. 

If the rough opening is not measured correctly, it's possible the windows you bring home won't fit into the space. The new windows could be too large, too small, or too deep for the window space. Windows that don't fit properly can lead to drafts, leveling issues, and other problems. 

When you measure for rough openings and replacement windows, make sure you get windows that are a couple of inches narrower and shorter than the rough opening. The depth of the window can be the same as the opening or smaller, but not larger.