Calculate joists, decking boards and footings for a timber deck.
Board count depends on the pitch rather than the width alone, because each board carries a drainage gap. Footing count comes from the span limits of the beams and joists rather than from the deck area. Omitting the board gap understates board count by around 4 per cent, and gaps are not optional because timber and composite both need drainage and movement room.
Deck
Boards = deck width ÷ (board width + gap); joists = length ÷ spacing + 1
Boards = deck width ÷ (board width + gap); joists = length ÷ spacing + 1 Board count depends on the pitch rather than the width alone, because each board carries a drainage gap. Footing count comes from the span limits of the beams and joists rather than from the deck area.
Omitting the board gap understates board count by around 4 per cent, and gaps are not optional because timber and composite both need drainage and movement room.
This calculator takes 5 inputs: Deck length, Deck width, Joist spacing, Decking board width, Gap between boards. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.