You aren’t. The only way to compare compressor performance is through the use of SCFM.
It’s not like meters & feet that have a valid conversion factor. CFM is like oranges and SCFM are apples. You can’t convert an apple to an orange. They’re just different. Mfg who only publish CFM ratings are doing it purposely because their SCFM performance isn’t good vs the competition at the same price point or power levels.