How To Measure Replacement Windows
Ordering the replacement windows is fairly straight forward if you know what dimensions you’ll need. You need to measure the height and width of the existing window opening.
Step 1 – Measure Width: First you need to measure the width of the window. See Figure 1 which shows how to measure the width of the unit between the left and right jambs.
If your house had replacement windows previously then it’s likely you’ll have a plastic or aluminum jamb liner where the parting stop and jamb are shown in the photo above. Later in the article I’ll show a photo of a that jamb liner. I bring this up because the jamb liner is typically about 3/8 to 1/2 inch thick and you need to base your width on the fact that the jamb liner will be removed.
Once you’ve measured the width shown above you’ll want to order the replacement window approximately 1/4 inch narrower (each manufacturer actually recommends how much narrower to use).
Step 2 – Measure Height: Next you need to measure the height of the replacement window. Most (but not all) existing windows will have a sloped sill. This is important to note because you want to be sure to measure the “least” opening which occurs at the top of the sill. See Figure 2 for a sketch on how to measure the height.
Step 3 – Unit Depth: The last dimension you need to check is the distance between the outside blind stop and the inside stops. Most older windows were built with a dimension of 3-1/4 inches to 3-1/2 inches. In order for standard replacement windows to fit you need a minimum distance of 3-1/4 inches (see figure 3).