Deck calculator
Deck Calculator — Decking Boards, Joists, Beams (2026)
How many decking boards, joists, and beams do I need? Inputs deck length and width, board width (5.5" composite or 5/4x6), joist spacing (16 or 24 in on-center), and stock board length (8/10/12/16/20 ft). Free, mobile-first.
Pricing
Enter deck length and width above to see board count, joist count, and beam count.
Decking, joists, beams & fasteners on Amazon
The calculator above generates board, joist, and beam counts for the deck footprint — stock the fasteners, hangers, and footing tubes below to actually build it.
- 5/4x6x16 pressure-treated decking board ↗
Stock length matches the calculator input — order one extra per row for cut waste.
- Composite decking board (Trex / similar) ↗
Pricier up front; no splinters and no annual staining.
- 2x8x12 pressure-treated joist ↗
Pairs with the 16 in on-center joist spacing default.
- 2x10x16 pressure-treated beam stock ↗
Stock for a built-up (2-ply) beam carrying the joist ends.
- Concrete pier footing tube (12 in × 4 ft) ↗
Use with the deck calculator footings — keeps wood off bare soil.
- Simpson Strong-Tie LUS joist hanger ↗
Two hangers per joist-to-beam connection — match them to the joist depth.
- 1-1/2 in joist hanger nails (5 lb box) ↗
Never substitute framing nails in hangers — they crack the galvanized coating.
- GRK R4 composite decking screws (5 lb) ↗
Star-drive, self-countersinking — one box covers ~300 sq ft of decking.
Or shop the same list on Home Depot Pro
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Gallons of paint and primer for railings, stairs, or the trim around the same project.