how deep does electrical box need to be to accomodate this outlet?

Assuming this is for a new dryer circuit, you cannot use this receptacle. Since 1996 electric dryer and range circuits have been required to be 4-wire circuits with 4-wire receptacles. The 3-wire dryer receptacle you have chosen is for replacement purposes only of an existing 3-wire dryer receptacle. For the 4-wire dryer receptacle I would recommend using a 1900 box (4" square) with a 1/2" recess, 2-gang plaster frame.