Troutman Sanders will merge with a 100-lawyer Washington firm, Ross, Dixon & Bell, gaining offices on the West Coast and in Chicago.

The deal, effective Jan. 1, will make Troutman Sanders a 750-lawyer firm, with about 1,700 total employees. Troutman’s chairman, Robert W. Webb Jr., said it will double the size of the firm’s Washington office, from 58 to 105 attorneys.