Free deck calculator estimates decking boards, joists, fasteners and material cost from your deck area and board dimensions.
Building a deck means ordering boards, joists and fasteners from three different supply lists - and every deck builder knows the pain of running out of boards two rows from the edge. This calculator turns your deck dimensions into concrete numbers: decking boards, joists, fasteners, concrete footings and a cost estimate.
Enter the deck length and width, the board size you plan to use, and the joist spacing. The calculator adds a waste allowance for cuts and damaged boards so your order covers the whole job, and estimates a footing grid (posts roughly every 2.4 m with beam rows about every 1.8 m) so you can budget the concrete too.
40 cm (16 in) on center is the most common spacing for residential decks and is the default reference in the IRC. Closer 30 cm spacing supports thicker loads or diagonal patterns, while 60 cm is used for lightweight composite boards on some systems - check the deck board manufacturer's requirements.
Most deck boards are installed with a 3-6 mm gap so water drains and boards can expand. The calculator treats the board width as the full installed width including the gap - enter the board width plus your intended gap.
A common rule is 2 screws at each joist, which gives about 4 fasteners per board for a typical 3 m board over 40 cm joists. Composite and hidden fastening systems use different counts - follow the product instructions.