When it comes to tillers, there is no one-size-fits-all answer. The depth that a tiller goes down will depend on the type of tiller, the soil conditions, and your own preferences.
That said, most tillers can be set to go down at least six inches below the surface of the soil. This is more than enough to loosen compacted earth and break up any clumps. If you’re working in particularly tough soil or want to get rid of larger rocks or roots, you may need to go even deeper.
Just be careful not to go too deep – you don’t want to damage any nearby plants or disturb underground cables or pipes!