Plus que vous ne pouvez l'imaginer
However, depending on the context, you might want to use a more nuanced phrase. Here are some other options:
* Bien plus que vous ne pouvez l'imaginer: Emphasizes the magnitude of "more"
* Au-delà de vos rêves les plus fous: More poetic, highlighting the impossible scale
* Un monde que vous ne pourriez jamais concevoir: Emphasizes the unfathomable nature of the concept
* Une quantité inimaginable: More concise and formal
Ultimately, the best translation will depend on the specific context and the desired tone.