Deck Calculator
Building a deck requires knowing exactly how many boards to buy. This deck calculator figures out the number of deck boards based on your deck's square footage, board width, and board length — including a 10% waste factor for end cuts and defects.
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Calculator
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Formula
Boards = ceil(Deck Area / (Board Width/12 × Board Length) × 1.1)
Board width is converted from inches to feet by dividing by 12. Multiplied by board length gives the area each board covers. Deck area divided by board area gives the raw board count. Multiplying by 1.1 adds 10% waste, then ceiling rounds up to whole boards.
How to use the Deck Calculator
- 1
Enter your deck area (sq ft)
Value should be in sq ft.
- 2
Enter your board width (in)
Value should be in in.
- 3
Enter your board length (ft)
Value should be in ft.
- 4
Read your results instantly
Results update in real time as you type.
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Choosing Deck Board Spacing
Deck boards should be spaced 1/8 inch apart to allow for drainage and expansion. For composite decking, follow the manufacturer's spacing recommendation — many require 3/16 or 1/4 inch gaps. Proper spacing prevents warping from moisture and allows debris to fall through. When calculating materials, this calculator uses the nominal board width; actual coverage per board is slightly less due to spacing.
Wood vs. Composite Decking
Pressure-treated lumber is the most affordable deck surface option but requires annual sealing and periodic staining. Cedar and redwood are naturally rot-resistant and attractive but cost more. Composite decking costs 2–3x more upfront but requires little maintenance and won't splinter, warp, or rot. Many homeowners find composite more cost-effective over a 15–20 year lifespan when maintenance costs are factored in.
Tips & Insights
Let Boards Acclimate
Store pressure-treated lumber on-site for 48–72 hours before installation so it can acclimate to local humidity. Installing wet PT lumber causes significant gaps as it dries.
Use Hidden Fasteners
Hidden fastener systems create a cleaner look with no visible screws and allow for better expansion. They cost more than face screwing but produce a higher-quality finish for composite and premium wood decking.
Run Boards the Long Way
Orient deck boards to run the longest dimension of your deck. This minimizes end joints, which are weaker and less attractive, and reduces the number of splices you need to make.
Worked Examples
Backyard Deck
62 boards needed with waste — covering 440 sq ft with a 10% waste buffer.
Front Porch
21 boards — a manageable weekend project with about 132 sq ft of coverage.
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Frequently Asked Questions
How much does it cost to build a deck per square foot?
Pressure-treated wood decks typically cost $15–$35 per sq ft installed. Composite decking runs $30–$60 per sq ft. Hiring a contractor vs. DIY can double the cost.
Do deck boards need to be pressure treated?
All framing and structural members (joists, beams, posts) must be pressure treated. Surface deck boards can be pressure treated, cedar, redwood, or composite depending on your preference and budget.
How long do deck boards last?
Pressure-treated pine lasts 10–15 years with proper maintenance. Cedar or redwood lasts 15–25 years. Composite decking typically carries 25–30 year warranties.
What size deck boards should I use?
5/4×6 (actual 1" × 5.5") is the most common deck board for residential use. 2×6 boards are also popular and more rigid for wider joist spacing. Composite decking comes in similar widths.
How far apart should deck joists be?
For 5/4 deck boards, joists should be 16 inches on center. For 2×6 boards, 16–24 inches on center is acceptable. Composite decking requirements vary; some require 12-inch joist spacing.
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