How much can Makarov grow? Makarov, master of fairy tail, has the power to turn into a giant. What size  can he accomplish? Is that the limit of his power or there's more to his skill?

An approximate size is also valid. No need to go into detail as apparently the exact size hasn't been confirmed.
We never see his size limit, but he can grow himself to the size of Tenrou Island



Another angle from manga



Makarov size compared to a ship