I need some lumber spanning information

I'm going to build a 20x30 patio at work. I want to use 4x12 beams running the 30 feet on both sides and in the center (6 15 ft beams total). I want to know how far a 4x12 will span between posts. This span will hold 2x6s on 16" centers, approximately 10 ft long. I'm hoping to just have 1 center post (posts will be 4x6) but I'm not sure the 4x12 will span that far (15 ft). Anyone know or can point me to where I can find out? This would be to comply with California Codes. I may have to use 4x14 to span that 15 feet but I'm not sure.