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How much does a deck need in materials?

Count decking boards, joists, beams, footings, screws, stair parts and railing for a rectangular deck, then price them.

Updated October 12, 2026 · fact-checked against official sources

Decking
Beams and footings (sizes come from your plan)
Height, stairs and railing
Your prices (replace these examples with local quotes)
Decking boards (16 ft, with 10% extra)
29 boards

For 192 sq ft of deck: 13 joists at 16 in on center, 3 footings and about 676 deck screws.

Deck area192 sq ft
Board rows × boards per row26 × 1
Decking before extra26 boards · 410 lin ft
Joists (12.0 ft long)13
Ledger + rim joist pieces2
Beam boards (1 beam)2
Posts and footings3 (3 per beam)
Screws (2 per board at each joist)676
Stairs: risers × height5 × 7.20 in
Treads · total run4 · 3.7 ft
Stringers (about 4.7 ft long)3
Extra boards for treads2
Railing · posts (about)37 ft · 9 posts
Material cost at your prices
$2,976
Decking (29 boards + 2 for treads)$1,240
Framing (17 pieces)$425
Footings (3)$120
Railing (37 ft)$1,110
Screws (676)$81
Materials total$2,976

Not included: joist hangers, ledger fasteners, flashing, hardware, blocking, stair stringer lumber, concrete, permits and labor.

This deck is more than 30 in above grade, so a guard (railing) is required under the IRC as summarized in DCA 6.

These stairs have 5 risers. DCA 6 (IRC R311.7.8) requires a handrail on at least one side of stairs with 4 or more risers.

Material counts only, not a structural design. Joist, beam, post and footing sizes must come from your local code (IRC Section R507 span tables or the AWC DCA 6 guide) and your building department.

How the calculator counts a deck

The calculator assumes a rectangular deck with joists running out from the house and decking boards running along it, across the joists. It counts pieces; it does not size them. Joist, beam, post and footing sizes come from your local code and plan.

  1. Decking rows: deck depth in inches ÷ (board width + gap), rounded up. Each row needs the deck width ÷ board length boards, rounded up. Diagonal decking is counted by total linear feet instead.
  2. Joists: deck width in inches ÷ joist spacing, drop the fraction, plus one for the end.
  3. Screws: two where each board crosses each joist, as DCA 6 specifies.
  4. Footings: for each beam, width ÷ post spacing rounded up, plus one.
  5. Stairs: height ÷ 7¾ inches rounded up gives the risers; treads are one fewer, because the deck is the top step.

Worked example

A 16-by-12-foot deck attached to the house, 36 inches above grade, with 16-foot boards that measure 5½ inches wide, ⅛-inch gaps and joists 16 inches on center:

  • Area: 192 sq ft
  • Rows: 144 ÷ 5.625 = 25.6, so 26 rows of one 16-foot board, and 29 boards with 10% extra
  • Joists: 192 ÷ 16 + 1 = 13 joists, each 12 feet long, plus a ledger and a rim
  • Screws: 26 rows × 13 joists × 2 = 676
  • One beam with posts every 8 feet: 3 footings (a freestanding deck adds a second beam at the house, so 6)
  • Stairs: 36 ÷ 7.75 = 4.6, so 5 risers of 7.2 inches and 4 treads, for a 44-inch run with 11-inch treads. Five risers means the stairs need a handrail
  • Railing: 12 + 16 + 12 feet of open sides minus a 3-foot stair opening = 37 feet
Rules the calculator flags
RuleValueSource
Fasteners per board at each joist2AWC DCA 6
Gap between decking boardsabout ⅛ inAWC DCA 6
Decking angle to joists90° to 45°AWC DCA 6
Each decking piece bears on at least3 joistsAWC DCA 6
Guard required when deck is more than30 in above gradeDCA 6 / IRC R312.1
Maximum stair riser7¾ inIRC R311.7.5.1
Minimum stair tread10 inIRC R311.7.5.2
Minimum stair width36 inAWC DCA 6
Handrail required on stairs with4 or more risersDCA 6 / IRC R311.7.8
Cut stringers, if only cut stringers are usedat least 3AWC DCA 6
Footing depth12 in below grade or below frost line, whichever is deeperAWC DCA 6
Source: AWC DCA 6 (2015 IRC version); Knox County 2018 IRC stair handout

Edge cases

  • Board joints. If the deck is wider than one board, plan joints so they land on joists, and each piece still bears on at least three joists.
  • Composite and PVC decking. These products set their own gap and maximum joist spacing. Use the numbers from the maker's installation guide.
  • Diagonal boards. A board at 45° covers a longer span between joists, so check the decking's span rating before choosing wider joist spacing.
  • Odd shapes. Split an L-shaped deck into rectangles and run the calculator for each.

What to do next

Enter your footings in the concrete calculator as round columns to get bags of concrete, and contact 811 before you dig. If the deck needs a privacy screen or yard fence, the fence calculator counts posts and pickets. Plan for upkeep with the home maintenance budget calculator, and NYC owners can check when a DOB permit is needed.

Common questions

How many deck boards do I need?

Divide the deck depth in inches by the board width plus the gap to get the number of rows, then multiply by the boards needed per row. A 12-foot-deep deck with 5½-inch boards and ⅛-inch gaps needs 26 rows; at one 16-foot board per row on a 16-foot-wide deck, that is 26 boards before extra.

How many joists does a deck need?

Divide the length the joists are spread across (in inches) by the spacing, drop the fraction and add one. A 16-foot-wide deck at 16 inches on center needs 192 ÷ 16 + 1 = 13 joists. Joist size and maximum span come from your local code, not the count.

How many screws do I need for decking?

The American Wood Council’s DCA 6 guide calls for two screws (or nails) where each board crosses each joist. Multiply board rows by joists by two: 26 rows across 13 joists is 676 screws. Hidden fastener systems have their own counts.

When does a deck need a railing?

DCA 6, following the International Residential Code (R312.1), says decks more than 30 inches above grade need a guard. Your local code may add requirements, so confirm with your building department.

How many steps do my deck stairs need?

Divide the height from grade to the deck surface by the maximum riser height and round up. The IRC sets a 7¾-inch maximum riser and 10-inch minimum tread, so a 36-inch-high deck needs 5 risers of 7.2 inches and 4 treads.

Fact-checked October 12, 2026

From AWC DCA 6: 2 fasteners per board at each joist, ~1/8 in decking gap, decking from perpendicular to 45° to joists, each segment on at least 3 joists, guard required above 30 in, handrail on stairs with 4 or more risers [R311.7.8], non-ledger decks built with a beam at the house side, stairs at least 36 in wide, minimum 3 cut stringers, footings at least 12 in below grade or below frost line, decking spans usually 16 or 24 in. IRC 7 3/4 in max riser and 10 in min tread verified in the Knox County 2018 IRC handout. Knox County handout also confirms 2018 IRC R312.1 guards above 30 in. Worked example re-computed by hand (16x12 ft, 5.5 in boards, 1/8 in gap, 16 in o.c.: 26 rows, 29 boards with 10%, 13 joists, 676 screws, 3 footings, 5 risers of 7.2 in, 4 treads, 37 ft railing). Added a handrail flag and a second beam default for freestanding decks. A newer DCA 6 edition could not be checked (awc.org returned 403), so the 2015 IRC version is cited. ICC code text (codes.iccsafe.org) was not retrievable, so IRC R507 is named but not linked. The tool counts materials only; it does not size joists, beams or footings.

Sources

  1. DCA 6: Prescriptive Residential Wood Deck Construction Guide (2015 IRC version) · American Wood Council (accessed October 12, 2026)
  2. 2018 IRC Residential Stairs Information (R311.7.5 risers and treads, R312.1 guards) · Knox County (TN) Code Administration & Inspection (accessed October 12, 2026)
  3. 811 Before You Dig · Common Ground Alliance (accessed October 12, 2026)

General information, not legal, tax or financial advice. Rules change; confirm with the agency or a professional before you act.