How to find your air filter size
Look on the edge first
Almost every filter has its size printed on the cardboard frame, like 20x20x1. That's the size to order. Or snap a photo on our home page and we'll read it for you.
Why the numbers don't match your tape measure
The printed size is the nominal size, rounded to the inch. The filter itself is a little smaller so it slides into the slot. A 20x20x1 filter really measures about 19.75 × 19.75 × 0.75 inches.
No label? Measure it
- Measure the width and height of the old filter, not the slot, edge to edge.
- Measure the depth, the thickness of the frame.
- Round each number up to the next whole inch. That's your size.
If your measurements already land on whole inches, you may have a custom size. We make those too.