ABC will partner with the Newspaper Association of America (NAA) and Scarborough Research to join data for both media, as well as "pass-along" print readership figures that indicate secondary newspaper readings by individuals other than the buyer.
The change will take effect from September. Metrics ABC uses are monthly visits, unique users, page impressions, most popular sections and average duration per visit.
In the UK, ABC in 2004 ruled out combining print and online readership figures, but has combined figures for business-to-business titles and new quarterly group reports the bureau launched this spring include individual figures for each medium.
Demand for combined figures in the US has come from advertisers eager to weigh up which publications are worthy of receiving investment.
"As online advertising expenditures continue to grow, we're hearing from more publishers and online content providers that want to demonstrate the breadth of their audiences - in print and online - to advertisers and ad agencies," said ABC's president Michael Lavery.
"ABC's role is to bring transparency and accountability to audience measurements, regardless of the medium."
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