A standard Wii game disc holds roughly 4.7 GB (single layer) or 8.5 GB (dual layer) of data. A "highly compressed" file usually claims to reduce this size to anywhere from 100 MB to 1 GB.
Use WBFS (Wii Backup File System). This format "scrubs" junk data to reduce size while remaining playable on actual consoles. Fix Download Wii Games Highly Compressed
This is the most common format for real Wii consoles. It removes the padding to save space. If your game is in .iso format and taking up too much room, use Wii Backup Manager to convert it to .wbfs . A standard Wii game disc holds roughly 4