Google announced a tool called Ad Planner on Tuesday that lets advertisers find Web sites whose visitors match various demographic attributes.
"Enter demographics and sites associated with your target audience, and the tool will return information about sites (both on and off the Google content network) that your audience is likely to visit," the company said on its AdWords blog.
The tool, which was expected, also can show in detail how many people visit a particular Web site. The tool competes with offerings from companies including ComScore and Nielsen Online.
Right now, Google's tool is available by invitation only, however.
Data can be exported into a spreadsheet for further analysis or for import into Google's DoubleClick MediaVisor tool for managing ad campaigns, Google said.
The site is a more specific tool than the publicly available Google Trends tool, unveiled last week, that shows relative Web site traffic for various Web sites.