To level up your cards to the maximum level, very large quantities of cards are necessary. In this article you will get all the information about leveling.

Since I don't have so many cards to see all levels yet, @thomasgutierrez helped me. Thanks for that!

Okay, let's go...

Common

For one common card you get 2 XP. To get a common card to the maximum level you need 379 cards in total.

Start: Level 1 (0/2 XP) - the first card is worth 0 XP
2 Cards to complete Level 1 (2/2 XP) and hit Level 2 (0/4)
2 Cards to complete Level 2 (4/4 XP) and hit Level 3 (0/10)
5 Cards to complete Level 3 (10/10 XP) and hit Level 4 (0/20)
10 Cards to complete Level 4 (20/20 XP) and hit Level 5 (0/40)
20 Cards to complete Level 5 (40/40 XP) and hit Level 6 (0/80)
40 Cards to complete Level 6 (80/80 XP) and hit Level 7 (0/100)
50 Cards to complete Level 7 (100/100 XP) and hit Level 8 (0/200)
100 Cards to complete Level 8 (200/200 XP) and hit Level 9 (0/300)
150 Cards to complete Level 9 (300/300 XP) and hit Level 10 (MAX)

Rare

For one rare card you get 10 XP. To get a rare card to the maximum level you need 86 cards in total.

Start: Level 1 (0/10 XP) - the first card is worth 0 XP
2 Cards to complete Level 1 (10/10 XP) and hit Level 2 (0/20)
2 Cards to complete Level 2 (20/20 XP) and hit Level 3 (0/40)
4 Cards to complete Level 3 (40/40 XP) and hit Level 4 (0/80)
8 Cards to complete Level 4 (80/80 XP) and hit Level 5 (0/100)
10 Cards to complete Level 5 (100/100 XP) and hit Level 6 (0/200)
20 Cards to complete Level 6 (200/200 XP) and hit Level 7 (0/400)
40 Cards to complete Level 7 (400/400) and hit Level 8 (MAX)

Epic

For one epic card you get 25 XP. To get a epic card to the maximum level you need 32 cards in total.

Start: Level 1 (0/25 XP) - the first card is worth 0 XP
2 Cards to complete Level 1 (25/25 XP) and hit Level 2 (0/50)
2 Cards to complete Level 2 (50/50 XP) and hit Level 3 (0/100)
4 Cards to complete Level 3 (100/100 XP) and hit Level 4 (0/200)
8 Cards to complete Level 4 (200/200 XP) and hit Level 5 (0/400)
16 Cards to complete Level 5 (400/400 XP) and hit Level 6 (MAX)

Legendary

For one legendary card you get 100 XP. To get a legendary card to the maximum level you need 8 cards in total.

Start: Level 1 (0/100 XP) - the first card is worth 0 XP
2 Cards to complete Level 1 (100/100 XP) and hit Level 2 (0/200)
2 Cards to complete Level 2 (200/200) and hit Level 3 (0/400)
4 Cards to complete Level 3 (400/400) and hit Level 4 (MAX)

On this screenshot you can see four legendary cards at maximum level 4 and one legendary card at level 3:

Bonus: Tips for swapping cards

I give you some tips for swapping cards, which you should consider in order not to be disadvantaged.

Always swap Common for Common, Rare for Rare, Epic for Epic and Legendary for Legendary to avoid being disadvantaged. Disadvantaged also no other Steemians, play fair!
The summoners will probably play a central role. These are rare, but always exchange only summoners (rare) for summoners (rare) and not just any rare for a summoner (rare). Selenia Sky is also a summoner, but will be treated separately, you can see this in the next point.
There are nine Legendary cards, four of which are the four golden dragons. So always exchange only kites for kites, otherwise you will be disadvantaged. Selenia Sky once again stands out among the four dragons and is currently the most valuable card. Don't trade Selenia Sky for one of the other four kites, otherwise you will be disadvantaged. In principle, I recommend bunkering Selenia Sky.