What Are the Parts of a Window Frame?
Regardless of the type of windows you’re replacing, it’s important to know the key parts of a window frame before you learn how to size a window. Window manufacturers typically use these terms when specifying the measurements needed for a proper fit. Understanding these terms will help you measure accurately and ensure you purchase the right replacement windows the first time.
- Head: The head, also sometimes called the header, is the horizontal component at the top of a window frame. The head runs across the top ends of the two jambs (defined below) and the top edge of the upper window sash rests against the head.
- Jambs: The jambs are the vertical frame elements on either side of the window frame.
- Sill: The sill is the bottom horizontal component of a window frame. It runs across the bottom ends of the jambs and the bottom edge of the lower window sash rests against it.
Measure the Window Opening
You’ll want to take the following window size measurements for each window you plan to order. A Lowe’s associate can use these measurements to help you find the right windows for your openings.
Don’t have time to do this project yourself? Lowe’s can help. Check out our professional window replacement and installation service.
Step 1: Measure the Window’s Width
To find a window’s width, measure between the jambs at three points: top, middle and bottom of the window opening. Measure from the surface of the jambs, not from the trim strips or parting beads in your old window opening. Use the smallest of these three measurements to order the window.
If you have more than one window in the same room, for best results always measure each window independently. Although two or three windows in the same room may appear to be identical, they may not have the exact same dimensions.
Watch our video How Do I Use a Tape Measure? for tips on taking accurate measurements.
Step 2: Measure the Window’s Height
To find a window’s height, measure from the high point of the sill of your window (the surface that’s closest to the inside of the window) to the top of the window opening. Make three measurements: one at the left side, one at the center and one at the right side of the window. Use the smallest of these three height measurements to order the window.
Step 3: Measure the Window’s Depth
Now measure the frame or jamb depth from the inside face of the interior stop to the inside face of the exterior stop, as illustrated in the top-down image. Ignore all pulleys and parting strips when measuring for depth dimensions, as they'll be removed for replacement window installation.
There must be at least 3-1/4 inches of depth between the interior stop and the exterior stop to accept the depth of the replacement window.
Step 4: Check for Square
Measure from a top corner of the frame — where the head meets a jamb — diagonally across the opening to a bottom corner — where the opposite jamb meets the sill — and note the measurement. Measure diagonally from the other top corner to the other bottom corner. Compare the measurements. Replacement windows will typically allow for these measurements to be different by up to 1/4 inch.
If the measurements of the windows are different by more than 1/4 inch, you may need to note an adjusted width measurement. Run a level from one top corner of the frame to the bottom corner. Keeping the level within the frame, adjust it until it indicates a plumb line with the plumb bubble centered between the lines in the indicator window. Note the distance you had to move the level. Use this to update your smallest width measurement to create an adjusted width.
Expert Tips on Window Measurements & Replacement
- Choosing the correct replacement windows requires precise measurements to ensure a perfect fit. Make sure the measurements of the windows are accurate before ordering new ones or attempting installation.
- After you’ve made your measurements, record them and keep them handy.
- Before you attempt to replace your windows, make sure the window frames are in good condition. As you remove the old windows, look out for rot, brittle wood or water damage.
- Consider replacing your windows with energy-efficient windows to save on your energy bill and increase your home’s resale value.
Measuring for Replacement Windows
You want to save time and money by getting accurate window measurements before ordering replacement windows. It’s a task that you’re ready to take on as your next do-it-yourself (DIY) project. However, if it’s a level of DIY you feel you’re not ready to handle, we understand. Let Lowe’s do the work for you. Our professional window replacement and installation services can handle everything from measuring to installation and it starts with a free consultation. Or stop by your local Lowe’s and speak with a Red Vest associate who will help you get started.