I find that the Honeywell Pre-Filters cut-to-size is very easy to use. It comes with a template. Simply cut template along the dotted line for the pre-filter size needed. Place template on top of pre-filter and cut pre-filter to size. Depending on the type of unit you have, you get between 1 to 12 filters. I find this to be economical. I recommend the Honeywell Pre-Filters cut-to-size.