29 boards
Deck Calculator
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.
Material ListDecking boards to buy Pier concrete Waste-adjusted concrete Bag count Risers Treads Steps on stringer Stringer length
“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.
Deck footing counts and spacing
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.
Deck layout, footings, and stairs
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
Deck area, joist span lookup, pier concrete, decking board count, and baluster spacing from deck length, width, and layout.
You'll need 29 decking boards and 6 piers for this 192 sq ft deck.
You'll need
Deck result
0.58 cu yd
Detail values
- Deck area
- 192 sq ft
- Total load
- 9,600 lb
- Max joist span
- 142 in
- Minimum joist size
- 2x8
- Span lookup status
- Verified table row found
- Pier concrete
- 0.58 cu yd
- Decking boards
- 29
Assumptions
- Verified span table load basis: 40 PSF live load and 10 PSF dead load
- Species group: Southern Pine
- Joist mode: Auto recommend minimum size
- Decking material: Wood
- Max baluster opening: 4 in (editable; 4 in is the standard IRC guardrail-opening rule)
Formula details
- Deck area: deckLength x deckWidth
- Total load: area x (deadLoadPsf + liveLoadPsf)
- Span lookup: Use verified AWC DCA 6 Table 2 row for species, joist size, and spacing.
- Decking board count: ceil((deckArea / boardArea) x (1 + wastePercent))
- Pier concrete volume: Reuse round concrete footing calculation from Sprint 1 and multiply by pier count.
- Baluster count and gap: count = ceil(runInches / (balusterWidth + maxOpening)); gap = (runInches / count) - balusterWidth
Solves the gap so it never exceeds the standard 4 in IRC guardrail-opening rule, evenly distributed across the full run.
Concrete
Standalone footing concrete volume and optional bag count for the deck's piers, using the same pier fields as Deck above.
Order 0.1 cu yd of concrete for this pour.
Order
Concrete result
0.1 cu yd
0 bags
Warnings
- INFO Material estimate only. Footing depth, size, reinforcement, frost depth, and bearing capacity must be verified locally.
Detail values
- Cubic feet
- 2.36
- Cubic yards
- 0.09
- Waste-adjusted cubic yards
- 0.1
- Bag count
- 0
- Effective depth (incl. frost line)
- 3 ft
Assumptions
- Concrete density for bag estimate: 4050 lb per cubic yard
- Bag mode enabled: No
Formula details
- Rectangular volume: length x width x depth
- Round volume: pi x radius^2 x depth
- Cubic yards: cubicFeet / 27
- Bag count: ceil((wasteAdjustedCubicYards x 4050) / bagSize)
Stairs
Riser count, tread depth, and stringer length for a step-down from the deck to grade.
Plan for 5 risers at the code-max 7.2 in each, with 10.3 in tread depth.
Plan for
Stairs result
5 risers
4 treads
4 cuts
54.72 in
Warnings
- INFO This is a general reference only. Verify local code and field conditions before construction.
Detail values
- Risers
- 5
- Actual riser height
- 7.2 in
- Treads
- 4
- Tread depth
- 10.3 in
- Total run
- 41.2 in
- Stringer length
- 54.71 in
- Height of first step
- 5.7 in
- Typical step height
- 7.2 in
- Steps on stringer
- 4
- Stringer placement below landing
- 7.2 in
- Minimum stringer stock size
- 2x12
- Stair/rail bevel angle
- 34.95°
- Blondel check
- 24.7 in (within target)
- Stride comfort check
- 24.7 in (within comfort range)
Assumptions
- Code mode: IRC residential
- Solve mode: Automatic (code max riser)
- Tread depth source: Comfort-adjusted default
- Tread thickness: 1.5 in (default assumption)
- Stringer mount type: Standard
- Minimum stringer stock size: 2x12 (jobsite rule of thumb for typical residential rise/run; verify against your actual cut depth)
Formula details
- Risers: ceil(totalRise / maxRiser)
- Actual riser height: totalRise / risers
- Treads: risers - 1
- Tread depth: clamp(17.5 - actualRiserHeight, minTread, 11.25) or user preference
- Stringer length: sqrt(totalRise^2 + totalRun^2)
- Height of first step: actualRiserHeight - treadThickness
- Steps on stringer / placement below landing: risers - 1 cut into stringer, top of stringer sits one riser height below the landing
Standard mount lets the landing framing form the top riser; flush mount cuts every riser into the stringer itself.
- Stair bevel angle: atan(actualRiserHeight / treadDepth)
Joist and decking board estimating
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.
When a deck needs stairs
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.
FAQ
Why is there a separate Concrete section if Deck already shows pier concrete?
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.
Do I have to enter a deck height if I'm not building stairs?
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.
Can I fine-tune just the footing or stair numbers?
Yes. Flip Concrete or Stairs to "Manual entry" to edit its inputs directly without changing the deck layout or the other calculator.
Why does the joist span lookup say data isn't available for my combination?
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.
What changes when I pick composite decking?
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.
How is baluster spacing calculated?
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.
Disclaimer
Material estimate and general reference only. Verify local code, structural requirements, and manufacturer/engineering guidance before ordering or starting work.