Both the Xbox and the Pocket Edition recently hit sales milestones recently, which allow us to easily calculate total sales across all platforms:
PC/Mac: 8.7 million
Xbox: 5 million
Pocket: 5 million
Total: 18.7 million
In early December it was reported that the XBox version was selling 40-60K copies every week, and Notch himself tweeted that Minecraft sold 453k copies on all platforms on Christmas day.
In November, 2011 Minecraft had sold 4 million copies; in the fourteen months since then it has sold another 14.7 million across all platforms.
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