Deck Calculator
Deck boards, joists and screws from the deck size, actual board width, your gap and joist spacing, stock length and waste — geometry only, not a span table.
The number of boards (and boards per row when stock is short), joists at your spacing, screws at two per crossing, linear footage and an optional board cost.
Example: 16 × 12 ft with 5.5 in boards and a 1/4 in gap needs 26 rows (29 boards with 10 % waste), 13 joists at 16 in and 744 screws.
Rows across,
joists along.
How boards and joists are counted, what stock length does to the board count, what the screw count assumes, and why the page has no span table.
Boards
Boards run the length of the deck; the width is divided by one board width plus the gap, rounded up to whole rows. Use the actual board width (a nominal 2×6 is 5.5 in; a 145 mm composite is 145 mm) and the gap the maker specifies. When your stock boards are shorter than the deck, each row takes ⌈length ÷ stock⌉ boards and the page reports the offcut, which staggered joints can reuse.
Joists and fasteners
Joists run across the width at your centre spacing: ⌊length ÷ spacing⌋ + 1, so a 16 ft deck at 16 in centres has 13. Screws are counted at two per board–joist crossing; hidden-fastener systems use different quantities — take theirs.
Waste and cost
Waste is a percentage you choose, applied to boards and screws; none is assumed. Cost is boards times the price you enter, nothing else — beams, posts, ledger, hangers and finish are not included.
What the number does not settle
Joist span, spacing limits for a given board, beam and post sizing, ledger attachment and railing loads are structural and code matters; the page carries no span tables and makes no claim that a layout is adequate. Inputs stay in your browser; the same four anonymous usage counts as the rest of the site apply.