I'm planning to build a deck attached to the end of my house. It will be 12 feet out from the house. The posts will be 2 x 10" concrete blocks (to be covered with artificial stack rock). How far apart can my posts be. Is 12.4foot centers too far apart? This would cause about 11 foot of span between edges of posts. Joists connecting the post are to be 2x16". Joists from front to rear to be 2x10" with 16" centers. Thanks in advance for your response(s).

You might do better to check with where you are buying the material than rely what you find here. 2 x 16's would be rather stout, but likely expensive. You might be better to put in a third post and use lighter members. You are planning to use the common pressure treated lumber?

Thank you Labman for your reply and bringing the super adequacy to my attention. I actually want to use 2x10" supports between the posts with the same size joists. Yes, this will be pressure treated lumber. Is the span of the posts too wide? My reason for the distance is to reduce obstruction from lake view.

I am afraid not a lot of science goes into these things. Somewhere there should be a table for these things. As I said, material suppliers should be able to help. Another thing would be to go ahead with it as is except leave room for a second 2 x 10 outside of the first one. If the deck is a little springy, add another one.