Window manufacturers have a wider variety of standard window sizes than you might think. In fact, it may be easier to say that standard window sizes no longer exist! Each manufacturer has dozens or hundreds of standard sizes in their catalogs.
For homeowners, custom windows are rarely necessary because you can find standard window sizes to fit your existing window openings. On the other hand, custom windows do not necessarily cost more than pre-fab windows.
When the time comes to replace windows or add windows to an addition, homeowners can expect to find plenty of standard options as long as the window is not abnormally shaped — if you want a special window that is extremely tall and very slim, that’s when custom windows would be necessary.
How to Read Standard Window Sizes
Standard window sizes tell you the whole number measurement of the height and width. In some cases, manufacturers uses half-inch increments. The actual windows will be made slightly smaller than the listed dimensions to make installation easier. Window installers use flashing and shims to fit the window into the opening, flush and tight.
Some standard window sizes use a special code instead of listing the inches. The code is four numbers that reflect the width in feet and inches, followed by the height in feet and inches. For example, a 2’6” by 4’6” window might list as 2646.
The Most Common Window Sizes
The short answer on standard window sizes: typical residential windows including single- or double-hung windows and casement windows come in sizes of about 2’ to 3’ wide and 4’ to 5’ tall.
However, you can purchase windows in size increments of 2 to 4 inches, across a wide spectrum. A particular style of window from one manufacturer may have minimum measurements of 1’6” by 3’ and maximum measurements of 3’6” by 6’, for example.
Bay and bow windows come in much larger sizes, often up to 10’ or more in width. Fixed windows that do not open may also be larger.
Bottom line: standard window sizes exist for each individual window manufacturer, but not across the board. For most any window opening, though, your local window installers can help you select from a variety of standard windows.