How Wide Should Window Boxes Be

For the best visual effect, your window box should be at least as wide as the window but should not extend more than three inches beyond the trim on each side.

How deep and wide should window boxes be?

A minimum of 8 inches in depth and 8 inches from front to back is required to have enough room for a selection of plants. Larger–say a foot in depth and width–is even better, particularly if you want to include a lot of plants and want them to fill out enough to overflow the box.

How wide is a window box?

Since many traditional-style uPVC windows are around three feet long, almost every window box style is available in 30-inch and 36-inch lengths. Window boxes generally look best if they are the same width as your window, but there are exceptions to the rule.