2018 was an excellent year for Roku, with record results and solid progress towards our long-term vision of powering every TV in the world. As more than 3 million U.S. households cut the cord, Roku added nearly 8 million active accounts in 2018, increasing our total active accounts to more than 27 million at year end. We estimate that nearly 1 in 5 U.S. TV households now use the Roku platform to stream at least a portion of their TV viewing. While our growth has been impressive, we believe we are still only beginning to capitalize on the large opportunity streaming presents. We expect to reach $1 billion in revenue in 2019, by focusing on these key areas: increasing monetization per user and scaling the number of households using the Roku platform.

We believe that in the medium-term the most significant factor driving Roku's financial performance will be increasing monetization of our growing installed base. In the TV streaming world, viewer share is well ahead of TV ad budget share, but the rapid growth of our Platform revenue suggests advertisers are starting to respond. This anticipated spending pattern shift, combined with substantial growth in our ad inventory and audience reach, should drive sustained, rapid advertising growth.

Over the long-term, we believe active account growth will be the biggest driver of our P&L. We more than doubled our active account base between 2016 and 2018, and quadrupled the size of our Platform revenue from just over $100 million in 2016 to over $400 million in 2018. In the U.S. alone, our active account base would make the Roku platform equivalent to the No. 2 traditional pay TV/cable company.