Measuring for Window Boxes

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 Getting the correct sized window box for your window is critical to making sure it looks right. Most big box stores only carry one or two sizes making finding the correct size for your window a bit of an adventure. Because selection in local stores is often limited many people end up getting window boxes that are either too small or just don’t fit the window making the whole setup look awkwardly put together.    

The first step to getting a perfect look is considering that you may need custom window boxes. Now before you get worried that the cost will get too high it’s important to point out that while most local big box stores don’t carry a wide selection there are several online retailers that do carry a full range of window boxes and have many non-custom sizes that likely will fit your window without costing you a fortune. One such online retailer is Flower Window Boxes which offers their window boxes in 14 different standard lengths ranging from 2 foot all the way to 9 foot plus custom capabilities.   

The second step once you’re prepared to get the right look is to now figure out the measurement. To measure your windows for window boxes there are two standards in the industry worth mentioning and you will commonly see architects draw it up two different ways on blueprints.    

1. If the window box is on brick then measure the size of the brick opening and get a window box as close to that size as possible. If you can’t find the exact size online consider getting a custom size or the next size up within 4-6” longer. It is better to get a box slightly longer than the window rather than slightly shorter as the aesthetic proportions show better and look more accurate.   

2. If the window box is on siding then you will want to look to see if there is trim wrapped around the window. In most cases there is and you will want to measure from the far left outside of the trim to the far right outside the trim measurements. Basically you are measuring the window and the trim to get your measurements. The reason for this is twofold. First, when looking at the window from the street you typically see the whole unit (window + trim) and that is what catches your eye. So getting a box to match that measurement makes the most sense. 

And Secondly, most windows are frame out and attached to studs that surround the window. After the window is installed it is wrapped in trim to cover up the stud and the siding butts up to the trim. What this means is that by getting a box that goes to the outside of the trim you give yourself the option of attaching the window box to those known studs that frame the window out. This makes for an easier and better installation that will save you a lot of headache.   

Sometimes there is still doubt as to what size window box you should get. For example, on some smaller windows with dark shutters and light-colored siding the rule is sometimes modified. Most windows appear dark from the street and having dark colored shutters can exaggerate the size and feel of the window making it feel bigger than it is.  This effect is magnified on small windows like 36” wide since 15” shutters on either side can make the window seem like it is more like 6’ wide instead of 3’wide. For this reason I recommend the paper towel trick. Simply take a roll of paper towels and roll it out to 3’ then cut with scissors. This now gives you a 3’ rectangle that you can tape under the window and view from the street. 

This is where you may get a sense of the space the window box will take up and so it will help you get a feel for whether or not you are getting the correct size. Quite often when shutters are present I recommend getting a window box 6” longer than otherwise. This helps balance the effect created by the shutters. Hope this helps, Good luck!    

About the Author

Matthew Buquoi is the owner of Flower Window Boxes, an ecommerce window box company.  He has nearly two decades of knowledge in the window box industry.