depending on region and release type. For preservationists or collectors, the "Complete Rom Set" varies significantly in size based on whether it is compressed, encrypted, or includes all regions and digital-only content. Total Library Size Estimates
To give you a more concrete idea:
Note: These figures are for decrypted (.3ds) or installable (.cia) formats. Encrypted dumps are smaller but less useful. 3ds Complete Rom Set Size
By contrast, early 3DS games like Super Mario 3D Land or The Legend of Zelda: Ocarina of Time 3D are usually under 512 MB. depending on region and release type