Worldwide mobile advertising revenue is expected to reach $11.4 billion in 2013, but small businesses have few tools to fully understand the value of mobile advertising.

Google announced yesterday the launch of  Full Value of Mobile Calculator, a free tool that measures how much money mobile advertising actually brings in.

Here's how it works. Businesses upload data from Google’s AdWords or from their mobile websites and input them into the step-by-step calculator. The tool goes through five potential outcomes of a mobile advertising campaign: in-store sales, phone calls, app downloads, cross-device purchases, and sales on mobile site. It takes about 30 minutes to complete the calculation, according to Google.

For instance, to calculate the value of in-store sales started on mobile, a user enters the number of clicks, the percentage of visits out of total clicks, the percentage of purchases out of total visits, and the average value of an in-store purchase. (If you do not know the exact data, the calculator provides a list of estimates based on different industries.)

After you input all the data, the tool will automatically calculate two benchmarks: the mobile site value and the value of all mobile advertising conversions. 

Google’s launch of the Full Value of Mobile Calculator came on the same day when Yelp announced a new feature, which was based on a Boston Consulting Group study, to quantify the site’s value to small businesses.