What do you mean by shards? Could you clarify a bit more? If you mean Skill points (the things you use to level up characters Skill trees)
Then here’s a list
Bronze: 1 skill point per level up
Silver: 2 skill points per level up
Gold: 5 skill points per level up
Diamond:? Not sure but the pattern is doubling up so probably 10 skill points
If you mean how many shards for an elemental essence then you need 3000 individual shards of the same element as the fighter you want to level up- hope that somewhat helped!