Each Garden Grid square measures ~11”x11” from tube center to tube center. We size the Garden Grid to fit the interior dimensions of most garden beds. For example, a 4x4 Garden Grid measures ~44"x44". This is because a common garden bed with 4'x4' exterior dimensions will have a smaller interior size, due to the thickness of the garden bed materials. Some materials are 6mm thick, and some are a few inches thick, so we size to accommodate as many variations as possible. If your garden bed sizing does leave a large gap beyond the Garden Grid™, a popular modification is to twist the perimeter tubes around so they spray outward and water the extra space. Here's a quick video from our co-founder, Bryan, showing this and a link to our full article to learn more: https://gardeninminutes.com/extra-space-garden-grid-tip/
If you're wondering if you can use The Garden Grid™ for Square Foot Gardening, yes you can! It's recommended. You can find more info about that topic here: Can You Use The Garden Grid™ For Square Foot Gardening?