WoodCalc Pro

Deck Calculator

Size your deck and get a full material list: decking, joists checked against the IRC span table, beams, posts, footings, screws and concrete, priced with your local numbers.

Deck size

16' or 192

Decking

Framing

Your prices ($) for the cost estimate

Deck boards

28× 16 ft

Deck area
192 ft²
Rows of boards
26
Joists
13 × 12 ft
Rim & ledger
56 lin ft
Beams
1 × 16′ 0"
Posts / footings
3
Concrete
12 bags
Deck screws
680 (3 boxes)
Material estimate
$1,255.00
Per sq ft
$6.54
  • Joist span 11′ 10 1/2" vs 14′ 0" max
    IRC Table R507.6, 2×10 Southern pine No. 2 at 16" o.c.

Excludes railings, stairs, joist hangers, ledger fasteners, flashing and post bases. Decking includes 7% waste.

Need stairs down to the yard? Run the stair calculator. For the joist table and post spacing, see the deck joist span calculator.

How the deck material list is figured

  • Deck boards: rows = projection ÷ (board width + gap), boards per row = length ÷ board length, both rounded up, plus waste.
  • Joists: length ÷ spacing + 1, running from the ledger (or front beam) out to the beam. Span is compared to IRC Table R507.6 for No. 2 lumber, 40 psf live load.
  • Beams and posts: one beam for a ledger-attached deck, two for freestanding. Posts at your spacing along each beam, one footing per post.
  • Concrete: footing volume π × r² × depth, at 0.6 ft³ per 60 lb bag.
  • Screws: two per board per joist.

This is a planning list, not a structural design. Most US jurisdictions require a permit for decks attached to the house or more than 30" above grade, and the American Wood Council's free DCA 6 Prescriptive Residential Wood Deck Construction Guide is what many inspectors check against.

Ask the shop

Stuck on a detail? Ask a question about this job. Your current inputs and results are sent along so the answer fits your numbers. AI answers can be wrong, so double-check anything structural with your building department.

Questions people ask

How many deck boards do I need?
Divide the deck width (measured along the joists) by the board width plus the gap. For 5½" boards with a 3/16" gap that is 5.6875" per row: a 12 ft (144") deck needs 26 rows. Then multiply rows by the number of boards per row, which depends on deck length and the board length you buy. Add 5–10% for waste, more on diagonal layouts.
How much does it cost to build a deck?
Materials for a pressure-treated deck typically run $15–$25 per square foot in 2026 and $30–$60 for composite, before hardware, railings, stairs and permits. Pro-installed decks usually cost two to three times the material price. Enter your local board prices above for a real material number.
How many screws do I need for a deck?
Two screws per board at every joist. For 16" joist spacing that works out to about 350 screws per 100 sq ft with 5½" boards. Buy 5 lb boxes of 2½" coated deck screws (roughly 350–400 per box) or hidden fasteners at one clip per joist crossing.
What gap should I leave between deck boards?
For kiln-dried or composite boards, follow the manufacturer: usually 3/16" to 1/4". Wet pressure-treated lumber shrinks as it dries, so install it tight or with an 1/8" gap; it will open up. Leave 1/8"–3/16" at butt joints.
What joist spacing do I need for decking?
IRC Table R507.7: 5/4 (1") wood decking may span 16" when laid perpendicular to joists and 12" on a 45° diagonal; 2× decking may span 24" perpendicular and 16" diagonal. Composite and PVC decking spans are set by the manufacturer, usually 16" (12" for diagonals and stair treads).
How deep should deck footings be?
At least 12" below undisturbed soil and below your local frost line (IRC R507.3.2), which ranges from 12" in the South to 48" or more in the northern US. Your building department publishes the local frost depth.

Related calculators

Deck Joist Span CalculatorMaximum joist span and spacing from IRC Table R507.6.Stair CalculatorRisers, treads, stringer length and angle, checked against the IRC.Fence CalculatorPosts, rails, pickets and concrete for a wood fence.IRC Stair Code CheckerCheck an existing or planned stair against IRC R311.7 and baluster spacing.