Proper filter for this fan?

I was wondering if anyone could shed some sort of light on this subject. I have this 6 inch inline fan which i have no idea how many cfm it pushes. I'm going to say alot. It definitely creates a wind. Problem is i have no idea what size filter to hook it up to because i have no idea how many cfm i'm pushing. Is there maybe a happy medium i could use blindly or something?

The carbon filters come in sizes by inch 6inch exhaust fan 6inch filter.

lio is right normally 6in filter to 6 in fan most 6 in fans are 440cfm roughly then remember when you put a filter on it it drops like 20% or something depending on the size of your room may want to step up the fan and filter to 8 inch and get a speed controller will increase the life of the fan not running on full all the time.