Many Waterproof MP3 players' storage capacities are between 2GB to 8GB. Again, It depends on the model of the gadget. Some MP3 Players don’t operate Bluetooth properly underwater, so that’s why you’ll need a storage capacity to download music.
Every song has its length and sound quality, so song size varies. A rough estimate is you can download at least 230 songs on the device.
Moreover, the waterproof MP3 players contain 2GB of space to store up to 500 tracks. 4GB of space of the MP3 player can store up to 800-1000 tracks, and 8GB can keep more than 2000 tracks. It depends on your requirements which one suits you. However, the less storage gadget will be more efficient for you.