A similar pattern has continued during January 2011 with 115 ebooks being sold for every 100 paperbacks.

The figure only relates to the US market and the number of ebooks sold on Amazon’s own e-reader device, the Kindle, which now accounts for 41.5 per cent of the e-reader market. Amazon is expected to sell more than eight million Kindles this year, up from 2.4 million last year, according to Bloomberg.

The figures exclude any free ebook download offers but include those made via the free Kindle iPhone app and tablet and desktop apps.

Amazon chief executive Jeff Bezos said, “Last July we announced that Kindle books had passed hardcovers and predicted that Kindle would surpass paperbacks in the second quarter of this year.

“So this milestone has come even sooner than we expected – and it’s on top of continued growth in paperback sales.”