Decking calculator
Deck surface area with the board run worked out, so you can see the linear feet you are buying.
Decking
Deck surface area with the board run worked out, so you can see the linear feet you are buying.
Framing, footings and railing are separate. Boards figured at 5.5 in wide with a 1/8 in gap.
$1,386
308.0 sq ft of pressure-treated pine at $4.50 / sq ft
Free. No signup. The quantities carry over as line items.
How this decking calculator works
Deck surface area, with the board run worked out so you can see the linear feet you are actually buying. Framing, footings and railing are separate lines.
The formula
area to order = length × width × (1 + waste) · board run = area × 12 ÷ 5.625
Assumptions and defaults
| Board width | 5.5 in with 1/8 in gap |
| Default waste | 10% |
| Joist spacing | 16 in centres |
Pro tips
Buy boards long enough to span without a butt joint if you can. Butt joints on a deck need blocking under them and they are the first place rot starts.
Hidden fasteners cost more and take longer, but on composite they are the difference between a deck that looks built and one that looks screwed together.
Order framing separately and price it by the piece. Deck framing is usually more lumber than the deck surface.
Common questions
How many deck boards do I need?
Take the area, add waste, and divide by the coverage of one board — 5.625 in with the gap. The calculator shows both the linear feet and the 16 ft board count.
What is the best decking material?
Pressure-treated pine is cheapest and needs sealing. Composite costs two to three times more and needs nothing. Cedar sits between and looks best of the three when new.
How far apart should deck joists be?
16 in centres for most decking. Composite laid diagonally often wants 12 in — check the manufacturer's span table, it voids warranties.
How much waste for decking?
Ten per cent on a rectangle. More if the deck has angles, picture framing or a lot of short runs.