I use a 64GB card. To use the whole card I did the following: Use 'MiniTool Partition Wizard Free' (Windows) Delete all partitions on the card. Create a new partition selecting 'Primary' and 'Fat32'. You then have a 64GB (or there abouts) Fat32 partition and can copy the Recalbox files onto it. When Recalbox has installed you should have 57GB of free space for your Roms.