use your 4 feet tank Height  x Width  x Length then divide by 1000
and use that number to times 4  that that's your filter hour/ liter.... use that look for suitable filter...

p/s: normally they would recommended 2 times of your tank volume... but prefer overfilter ( watch out of tornado haha )

eg:

standard 2 feet tank ( 60 x 30 x 30 / 1000 = 54 liter )

54 x 4 =216 h/l flow rate i needed for my filter...
but i get a canister which 850 l/h it just suit nice on my 2 feet tank....
lol