Amazon Prime signed up 3 million new customers in December's third week. Pictured: Olly Murs visits Amazon to pick, pack and personally deliver surprise gifts to a family of fans using Amazon Prime Now one-hour service on Nov. 30, 2015 in London, England Eamonn M. McCormack/Getty Images for Amazon)

Streaming media and free delivery turned out to be popular must-haves this holiday season, driving more than 3 million new Amazon Prime subscribers in the third week of December, the online retail giant said Monday. The new subscribers to the premium service were busy binging on "The Man in the High Castle" or taking advantage of Prime's free and fast delivery.

While the numbers are impressive, it's difficult to say how impressive, because Amazon won't say how many Prime members it has in total.

The 3 million new Amazon Prime subscribers -- with membership costing $99 a year -- bring the total user base to "tens of millions of members worldwide," according to the company. Rival Netflix announced it added 3.62 million users in its third quarter of fiscal year 2015, bringing its total subscriber base to 69.17 million members.

"Over 200 million more items shipped for free with Prime this holiday, and members doubled their viewing hours of Prime Video, compared to last year, with the Amazon original series 'The Man in the High Castle' leading the way as the most watched TV season ever on Prime Video," Jeff Bezos, founder and CEO of, said in a statement.

Amazon also announced it doubled the number of Amazon devices sold during the holiday season. The Amazon Fire 7-inch tablet was the company's best seller.

Adele, not surprisingly, dominated the music side for Amazon. The British singer's latest album, "25," was the top album of the season, while "Hello," the only song from the album available on streaming sites, was the most popular song on Amazon Prime Music.

Amazon is not required to release any figures regarding total viewership or number of Prime members, which is why it's difficult to determine the success of the holiday season.

The company faced this problem when "The Man in the High Castle" was touted as the "most-streamed" original series last week. Network programming is monitored by third parties like Nielsen, but Netflix, Amazon and other streaming platforms are not subject to the same scrutiny.

As such, the latest news from Amazon indicates a great holiday season for the online retailer, but without much context.