Rule of thumb for fish food pellet size.

Small garden pond/tank.  I use goldfish sized multicolored pellets to feed the small local/feral fish and even the black larger sized pellets as some of the fish are a tad larger. But at the bottom are two or three comparatively Godzilla sized fish maybe the length of my hand. At what fish size does one go up to the 4mm-ish sized pellets that one buys at the temple for feeding carp.