Deck Flow's

Most decking calculators do area times price and stop there. That number won't tell you the joists are too far apart for the board you picked, or that your beam can't carry the span between posts, or that half your board joints are landing in mid-air instead of over a joist. Deck Flow works the deck from the footing up, the way you actually build it.

You give it the size and the height off the ground. It sets the joist spacing for your board thickness and direction — tighter for diagonal boards, on its own — and lays out the joists so the boards sit without sag and every joint falls over a joist, not between them. It checks the beam against the span and flags it when the posts are too far apart. It sizes the footings, the concrete, and the ledger fixing to the house with flashing so water doesn't get behind it.

Then it counts the real build. Boards across the joists with an expansion gap and the row lengths, staggered joints with a picture-frame border, screws or hidden clips down to the exact count so you're not driving back for a box mid-job. Board gaps, a fall away from the house, airflow underneath. Railing and steps. A material list and a cost estimate at the end.

It even holds you to the order: footings first, and the frame stays locked until the concrete's had time to cure, because a deck built on green footings moves.