Advocates of a new downtown Sacramento sports arena rolled out a study Thursday that puts an eye-popping number on the building's projected economic benefits: $7 billion over 30 years.

The study, commissioned by Mayor Kevin Johnson's arena task force, said the new facility would shower the region with $157 million a year. That includes spinoffs such as sales at restaurants and hotels, as well as $6.7 million in taxes.

The $7 billion estimate includes assumptions about inflation.