"Over the Rainbow/What a Wonderful World" reached No.12 on "Billboard"'s Hot Digital Tracks chart the week of January 31, 2004 (for the survey week ending January 18, 2004). It passed the two million paid-downloads mark in the US by September 27, 2009, and then sold three million in the US as of October 2, 2011. And as of October 2014, the song has sold more than 4.2 million digital copies. The song is the longest-leading number-one hit on any of the "Billboard" song charts, having spent 185 weeks on top of the World Digital Songs chart.