Window anatomy matters—and we have a breakdown of the major parts of a window.

By Real Simple Editors
Updated May 31, 2019
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Courtesy of Marvin

Being familiar with the different types of windows while picking out new windows or admiring previously installed ones is one thing, but what about the parts of a window? One aspect of appreciating what makes a window so great is knowing how all the different parts work together, but if you can’t tell the sash from the apron, you’ll have a hard time articulating what, exactly, you like about the window.

No matter where you do your window shopping—we’re partial to Marvin, the maker of master-crafted, premium-quality windows and glass doors—knowing how to point out the parts of a window that you like and don’t like will help you make the best window selection possible, changing the whole look and feel of your updated space in the process.

Learning how to hang curtains will help dress up your window selection, but picking the perfect windows—with the just-right sash and ideal grille placement—will make window treatments more of an accessory than a way to make up for not-quite-right windows. Once you’ve found the perfect windows with the right placement of window parts, you just need to learn how to clean windows, and you’ll have bright, mood-lifting light in your space all day, every day.

Parts of a window

Apron: A horizontal piece of trim underneath the sill.

Glass: Also called lite (industry terminology for the piece of glass used to create the window) or glazing. Four main kinds are available (see Window Glass Options).

Grille: Also called grid or muntin. Decorative cross pieces that divide the window into panes. Some grilles are suspended between the glass; others snap off for easy cleaning. Grilles for double-hung windows are named according to the number of squares they form (like six over six, as shown above). Not to be confused with mullions, which are vertical or horizontal pieces between adjoining window units.

Head: The horizontal piece that forms the top of the window frame.

Jamb: The pieces that form the top, sides, and bottom of the window frame (includes the head).

Lock: Most new windows come with locks, and there are upgrades, such as magnetic locks, that allow windows to lock automatically when closed.

Rail: The horizontal part of a sash.

Sash: The movable part of the window; the framework that holds the glass in place.

Sill: A piece that runs along the base of the window frame.

Stile: The vertical part of a sash.