Microsoft CEO Steve Ballmer predicts that a combined 400 million Windows Phone 8 and Windows 8 devices will be produced a year from now. He made the comment on stage today at Nokia’s Lumia 920 launch event.

What kinds of devices does he expect to see included in that 400 million? “That means Lumia. That means Surface. Devices introduced in Berlin last week. Those devices, I’m quite sure, represent the largest single opportunity for developers today,” he said.

Ballmer’s estimation includes all the phones running Windows Phone 8 like the Lumia 920 and 820, Samsung’s ATIV S, and likely upcoming devices from HTC. It also includes the slew of tablets, laptops, and hybrid devices running the Windows 8 OS.

“Perhaps more importantly than anything else, we bring a developer platform and a store that’s common to both Windows 8 and Windows Phone 8,” Ballmer said. He also noted that Microsoft has worked hard to standardize its platform, as well as help developers build and monetize their apps.

Steve Ballmer photo: Devindra Hardawar/VentureBeat