Finished look, then the bones
Size a backyard deck against the house wall. Switch to Bones to see joists, beams, posts, and footings. This is a shopping-list planner, not a structural design.
Decking boards38
Joists12
Posts / footings12 / 12
Deck area17.3 m²
Board waste6.4%
Rail length13.20 m
Joists span 3.60 m from the house. That is longer than a common 2.7 m planning rule of thumb, so the bones view adds a mid beam. Have a builder check spans, footings, and fixings. This is not an engineered design.