Enter your deck length, width, and pier layout once and get decking board count, footing concrete, and joist span data together — plus a stair layout if the deck steps down to grade.
“How much lumber for a deck” usually means three separate takeoffs: decking boards, footing concrete for the piers, and — if the deck isn’t flush with the door threshold — a set of stairs down to grade. This page runs all three from one deck layout. Each calculator below is the same one available on its own page — nothing here is a new formula, it is the Deck, Concrete, and Stairs calculators reading from a shared input set.
Pier count and spacing come from your joist layout and beam design, not from deck area alone — two decks of the same square footage can need a different pier count depending on joist span and beam size. This page uses the pier count, diameter, and depth you enter to run the standalone Concrete calculator’s exact round-footing formula once per pier, so the concrete number here always matches what you’d get running Concrete by hand with the same pier dimensions.
Joist span data (when available) comes from AWC DCA 6 Table 2, restricted to the load combination that table documents: 40 PSF live load and 10 PSF dead load. Outside that combination, or for species/size combinations not in the verified table, the calculator says so rather than guessing.
Enter deck length, width, joist and pier settings once. Pier diameter/depth/waste also drive the standalone footing Concrete result below; add a deck height only if this deck needs step-down stairs.
Deck area, joist span lookup, pier concrete, decking board count, and baluster spacing from deck length, width, and layout.
You'll need — decking boards and — footings for this — sq ft deck.
You'll need
On-centre run with a joist at each end -- the same fencepost count framing.ts uses for studs.
The crossing count is geometry: it comes from the board's own length, because a board shorter than the deck does not reach every joist. The two screws per crossing are not -- that is the ordinary face-screwed pattern, estimated, and NOT read from a fastening schedule. A hidden-fastener or clip system counts differently and is not modelled here.
boardArea is the board's bare face -- the gap between boards is not modelled, so a gapped deck counts roughly 2% more boards than it lays (a 1/8 in gap on a 5.5 in board).
Solves the gap so it never exceeds the 4 in guardrail opening of IRC R312.1.3 (no opening passes a 4 in sphere), evenly distributed across the full run. The section's stair-triangle and open-stair-side exceptions are not modelled here.
The band closes the joist ENDS, and the joists are spaced along the deck's length, so the band runs the length. A ledger deck bands the outer end only -- the house side is the ledger. The two side members are the outermost joists and are already inside the joist count, so they are not banded again.
Standalone footing concrete volume and optional bag count for the deck's piers, using the same pier fields as Deck above.
Order — cu yd of concrete for this pour.
Order
Volume yield per bag, as printed on the bag. NOT cured weight / dry bag weight -- that double-counts the mix water and over-orders by 12.5%.
Riser count, tread depth, and stringer length for a step-down from the deck to grade.
Plan for — risers at the code-max — in each, with 11.25 in tread depth.
Plan for
IRC R311.7.5.1: riser height not more than 7.75 in. The IRC sets no minimum.
The 11.25 in cap applies to the comfort default only -- it is the width of one board, not a code limit. IRC R311.7.5.2 sets a minimum tread depth (10 in here) and no maximum. The 17.5 in in the comfort default is the trade's rise-plus-run rule of thumb: estimated jobsite practice, NOT a code figure and not read from any published table.
Standard mount lets the landing framing form the top riser; flush mount cuts every riser into the stringer itself.
Decking board count divides total deck area by the coverage area of one board (board width times board length), then applies your waste percent and rounds up to a whole board — the same math as buying a fixed-length board from the yard rather than a per-linear-foot product. Waste covers trimming at the perimeter, picture-frame borders, and diagonal or herringbone patterns, all of which use more boards per square foot than a simple straight-run layout.
Joist mode lets you either auto-recommend the minimum joist size for your desired span (when the verified table covers your species/spacing combination) or manually pick a joist size and see its max span looked up directly.
Any deck that doesn’t land flush with an interior threshold needs a way down to grade. Enter the deck height above grade (not the total rise of an interior stair) and this page converts it to the inches-based total rise the Stairs calculator expects, then runs the same riser/tread/stringer solve available on the standalone Stairs page.
If the deck is flush with the door threshold and doesn’t need stairs, leave the deck height at its default or set it to 0 — the Stairs section will still compute a (trivial) result, but you can ignore it.
The Deck result includes a pier concrete total as part of its own load/footing context. The Concrete section below runs the same pier dimensions through the standalone Concrete calculator so you get its full quantities, formulas, assumptions, and warnings — the same transparency the standalone Concrete page gives any other job.
No. The Stairs section always computes something, but if the deck is flush with the threshold and doesn't need stairs, you can ignore that section entirely.
Yes. Flip Concrete or Stairs to "Manual entry" to edit its inputs directly without changing the deck layout or the other calculator.
The verified AWC DCA 6 Table 2 data only covers specific species group, joist size, spacing, and load combinations. Outside those, the calculator flags it rather than estimating a span it can't verify.
Board length switches to a picklist of standard factory-cut lengths (12/16/20 ft), and a warning appears if your joist spacing exceeds common manufacturer caps for the selected layout — 16 in o.c. for straight, 12 in o.c. for 45° diagonal.
Enter a railing run and baluster width in the Deck section and CrewMeasure solves the gap so it never exceeds the max opening (4 in by default, the standard IRC guardrail-opening rule), evenly distributed across the full run.
Material estimate and general reference only. Verify local code, structural requirements, and manufacturer/engineering guidance before ordering or starting work.