Google wants to prove to advertisers that there's a direct correlation between someone seeing a search ad and then going into a brick-and-mortar store.

The tech giant is rolling out a new tool today called "store visits" that gives marketers some insight into which types of search ads—which include local inventory and product listings ads—motivate people to go to a store.

Google's store visits tool uses an algorithm to estimate how many people went into a store as a result of seeing an ad within 30 days. In turn, advertisers are given anonymous data (meaning that it doesn't pinpoint specific users) that is collected from smartphone owners who have turned on their location history.

To qualify for the new tool, Google advertisers need to verify their location with the search giant and set up location extensions in an AdWords account. Store visit info is only available to U.S. advertisers and will gradually be rolled out within the next few months.

The data only gives brands an educated guess on how many people actually acted after seeing an ad, but it's already got the attention of Famous Footwear CMO Will Smith.

"The insight that we're getting from our partners at Google are really showing that the influence of online advertising is in fact not only getting people to shop on famous.com but to shop our stores across the country as well," he said.

Since beginning to test the ads a year ago, roughly 15 to 17 percent of the clicks on Famous Footwear's ads result in an in-store visit, the company said. With that insight, the brand is able to mix up the products it promotes and its in-store merchandising strategies by region through search campaigns.

Office Depot has also used shopping promos on Google to understand which products people look for online before going into a store.

The store visit tool is one of three measurement resources that Google has rolled out over the past year—collectively dubbed Estimated Total Conversions—that are aimed at helping marketers measure how search ads drive offline sales. Phone calls and cross-device measurement tools have previously been available to marketers as conversion tools.

The idea is to capitalize on brick-and-mortar stores, which still make up the majority of retail sales. Forrester Research predicts that e-commerce will grow $150 billion by 2018, but offline retail will increase by $300 billion.

Additional research from Google earlier this year found that 32 percent of consumers visit a store or make a purchase after seeing a location-based ad.

In a blog post, Google director of product management Surojit Chatterjee said, "Getting better insight into these new, complex purchase paths can help you optimize your online marketing programs, design better experiences for your customers and allocate budget more effectively."