You might be tempted to get the biggest screen that will fit in your backyard, but bigger screens require brighter projectors. If you already have your projector, you can use its lumens output to determine the biggest screen that will work, or you can work backward from the size of your ideal screen to figure out what projector you need to buy. To determine the size of the largest screen that will work with your projector, divide the projector’s ANSI Lumens by the desired foot-lambert total. It will work if the area of the screen you want, in square feet, is smaller than the number you calculated. If it’s bigger, the picture may not be bright enough. For example, let’s say your projector outputs 2000 ANSI Lumens, and you’re aiming for 60 foot-lamberts for a nice bright picture. You would divide 2000 by 60 and see that your screen could be up to 33.33 square feet. A 100-inch screen has an area of 29.6 square feet, so that would be just about the biggest screen you would want. You could select a bigger screen if you’re okay with a picture that isn’t as bright and clear or find a bigger projector.