We can't know for sure because sirius doesn't publish ratings like terrestrial radio. We do know sirius had put incentives in his contract where if they reached

We can't know for sure because sirius doesn't publish ratings like terrestrial radio. We do know sirius had put incentives in his contract where if they reached X more subscribers after Stern announced he was moving, he'd get a bonus. He met these almost instantly. More than his radio show, Stern also lost TV around the same time he switched to sirius.