"We've reached a tipping point with the new price of Kindle -- the growth rate of Kindle device unit sales has tripled since we lowered the price from $259 to $189," said Jeff Bezos, founder and CEO of Amazon.com in a statement. "In addition, even while our hardcover sales continue to grow, the Kindle format has now overtaken the hardcover format."
Given that Amazon has been selling hardcover books for 15 years and Kindle books for less than three years, Bezos characterizes the milestone as astonishing.
While Bezos's assertion that the Kindle device sales have tripled lacks meaning in the absence of a baseline figure to multiply times three, the Kindle book and hardcover figures do at least reveal something: The gap between hardcover sales and Kindle sales continues to grow.
Over the past three months, Amazon says that for every 100 hardcover books it sold, it also sold 143 Kindle books. Over the past one month, the ratio has been 180 Kindle books for every 100 hardcover books sold. And these figures do not include free Kindle books.
According to the Association of American Publishers, e-book sales grew 163% in May and 207% this year overall through May. Sales of adult hardcover books grew 43.2% percent in May. This is in terms of revenue rather than units.
Amazon says that Kindle book sales have been growing at an even faster rate than e-books in general.
Earlier this month, Amazon introduced a new version of the Kindle DX, a large screen variant of its portable reading device.
Amazon's Kindle Store carries over 620,000 books. Some 1.8 million free, out-of-copyright titles from before 1923 are also available for the Kindle.