These are a 4 inch filter but are in fact about 3 and 5/8 inches. So as a replacement for a Honeywell 4 inch filter which measures 4 plus inches, it leaves something to be desired.
The fit was a little tight and had to push hard to get it in, I measured it against the original filter that came with the unit, and it didn't seem to be any difference in size. The original filter had metal frame so I wonder if that meant a closer tolerance, the Filterbuy filter is cardboard framed which by it's nature has a higher friction coefficient.