When it comes to air filters, the larger dimension is usually printed first. This means that a 23 x 20 x 1 filter is a rectangle or perfect square. It's important to note that the “real” filter size, as measured by a tape measure, should be used when creating a filter with this tool, not a nominal filter size. If you're looking for a 23 x 20 x 1 filter, it's likely that the industry will call it a grid-cut filter.
It's also important to keep in mind that if you have pets, children, or people with allergies in your home or business, you should replace filters more frequently to maintain superior indoor air quality and reduce your energy costs. We've reviewed all of the best washable air filters for the home, so take a moment to read that article here. With the right information and tools, you can make sure your home or business has the best air quality possible.