It depends on the rarity of the card.
For 6*s, one Ambrosia will only give 2 extra level ups, requiring 10 for max level limit.
For 5*s, one Ambrosia gives 3 extra level ups, requiring 7 for max level limit.
For 4*s, one Ambrosia will grant 4 extra level ups, requiring 5 for max level limit.