AIR FILTER SIZE CHART
Here is a chart of standard-size air filters. Notice that the actual size of the filter is smaller than the size printed on the furnace air filter. It is always best to take the measurements yourself with an accurate measurement device.
Do you need some tips on measuring your air filter?
If your air filter size is missing from this list, you likely have an odd-size filter. A custom air filter may be a good option for you.