The old, outdated, and inefficient windows on your home have finally inspired you to replace them. The next thing that you need to know is how to measure for new windows because you don’t want to buy the wrong size. When you write down the measurements, follow the convention of listing width before height. All windows are sized according to this formula. Here, PJ Fitzpatrick’s window experts walk you through the measurement process step by step to make sure you get it right the first time.

Window Anatomy

To follow the directions for how to measure for new windows, you’ll need to know some basic terminology. The sides and top of a window opening are called jambs. The bottom area of the opening is known as the sill.

Detailed Instructions for How to Measure for New Windows

Measure the width from the inside edge of the side jamb next to the window to the other side jamb’s inside edge. Take a width measurement across the top, middle, and bottom of the window. Write each measurement down as you go.

1. Look at the 3 measurements and circle the smallest one. This will be the figure that you use for width.
2. Measure the window’s height from where the top jamb touches the window to the top edge of the sill. Take 3 height measurements down the left, center, and right of the window.
3. Find the shortest height measurement and circle it. This is the figure to use for height.
4. Measure the window opening’s depth. This figure derives from the distance between the interior trim edge to the exterior blind stop strip.
5. Get depth measurements from multiple locations and select the smallest figure for the depth measurement.

For windows that don’t open:

1. Measure from interior trim edge to glass.
2. Measure from exterior blind stop strip to glass.
3. Add the figures together.
4. Then add another 1/8 inch to account for the thickness of glass.

Note that a window opening must have a minimum depth of 3-1/4 inches to accommodate a replacement window.