LONDON -- Apple Music has converted 6.5 million subscribers into paying customers, the company's CEO Tim Cook has revealed, adding that another 8.5 million people are still using the three-month free trial.

Having 15 million people use a music streaming service that is just three months old is a huge success in anyone's book, but the figures pale in comparison to market leader Spotify, which boasts 20 million paying subscribers and a further 55 million who are using its free service every month. 

Apple, however, is already the second-biggest player in the market, ahead of Pandora's 3.9 million subscribers and the 3.8 million figure revealed last week by French-based service Deezer, which is seeking an IPO.

Speaking at a technology conference in California, Cook said: “I’m finding personally that I’m discovering a whole lot of music that I wasn’t listening to before. I think it’s fabulous, and to have over 15 million on there, and 6.5 million in the paid category, I’m really happy about it. And I think the runway here is really good.”

This is the first confirmation from Apple of how many people are signing up to its high-profile streaming service, which launched in June and was one of the main products of the $3 billion purchase of Beats Music just over a year ago. Apple's Eddy Cue had previously revealed that 11 million people had signed up for the free trial.

Apple Music is available to everyone with an Apple account and is available on iPhone and iPad as well as through iTunes on laptops and desktop computers. It allows users to stream a catalog of 30 million tracks as well as get access to curated playlists and the Beats One music station which is manned by DJs around the world.

Every users gets a free three-month trial when they first sign up, with Apple automatically checking the box for auto-renewal, meaning that many people would have been charged for Apple Music unknowingly once the initial three month trial ran out at the end of September. Some industry analysts predict this means we will see a drop in subscriber numbers after that one month of paid subscription.

In August, music industry analyst Mark Mulligan from Midia Research predicted that up to 50% of those 6.5 million paid subscribers could leave the service by the end of the first month. "The clever bit for Apple is that the total number of reportable subscribers, the ‘ever subscriber’ number, will be around 6 million because of those extra 3 million that accidentally paid for 1 month.  And because Apple Music should be growing at pace over the next 12 months, we’ll never even see the impact of that 3 million being wiped off the subscriber count, with them quickly replaced by new additions."