If you're wondering what size binder you will need for a Mega Evolution Master Set with no cards stacked on top of eachother, we recommend a 9-pocket binder with 360 pockets.

 

Here's a confirmed breakdown of the Mega Evolution set:

• 127 Numbered Base Cards

• 117 Reverse Holo Base Cards

• 56 Secret Rare Cards

• 2 MUR (Mega Ultra Rare) Cards
   

Optional Extras:​

• 6 Stamped Promo Cards

• 2 MEP Promo Cards

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In total, a complete Mega Evolution Master Set contains 302 unique Pokémon cards.