Advertisers and ad agencies have long yearned for a system that standardizes ratings across both TV and Internet ads, and today Nielsen launched its cross-platform advertising measurement service with GroupM.

The cross-platform ratings tool, which is called the Nielsen Cross-Platform Campaign Ratings, combines Nielsen’s traditional television ratings with its online campaign ratings in order to give advertisers a cohesive look at how their ads are doing in both environments.

The service, which will be available to other advertisers, provides clients with total and overlapped reach and frequency of their marketing campaigns.

GroupM and Nielsen will each contribute resources and expertise to create Cross-Platform Campaign Ratings and make it available to GroupM clients. The two companies will also work together to develop new measurement tools that extend beyond TV and online to other platforms.

“Our advertiser clients increasingly recognize that traditional television advertising and online video advertising must work together,” said Rino Scanzoni, GroupM’s chief investment officer. “It’s vital that we have consistent measurement, and that’s our goal in working with Nielsen.”

In the past, cross-platform measurements were unattainable because TV and Web ad campaigns used different metrics.

“Cross-platform metrics are essential to both buyers and sellers of advertising,” said Steve Hasker, president of media products and advertiser solutions for Nielsen. “Every day, we’re hearing from advertisers, online publishers, TV networks and agencies that a better system of measurement is required. Through working closely with GroupM and others in the industry, we believe we can help create best practices that will benefit the entire ecosystem.”