Decking Calculator

Planning a deck build starts with knowing exactly how much lumber to buy — the Decking Calculator takes your deck dimensions and board specs to tell you how many boards you need. Enter your deck length and deck width, then select your board size, joist spacing, decking angle, and standard board length to get your total boards needed, boards with waste, fasteners, and linear footage. Add a material cost per sq ft to also see your estimated material cost.

ft
ft
10 %
5 %20 %

Recommended 10-15% for cuts and mistakes

Optional: Enter cost to calculate total material cost

Results

Total Boards Needed

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Total Square Feet

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Boards with Waste

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Fasteners Needed

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Estimated Material Cost

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Linear Feet of Boards

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More Construction Tools

Frequently Asked Questions

How many deck boards do I need for my deck?

The number of deck boards depends on your deck size, board dimensions, and layout angle. For a standard 16x20 deck with 5.5" boards, you'll need approximately 58-65 boards including waste factor.

What are the most common deck board sizes?

The most popular deck board sizes are 5/4"x6" and 2"x6" for width, with lengths typically available in 8', 10', 12', 16', and 20' options. The 5/4"x6" boards are most common for residential decking.

How much waste factor should I include when ordering deck boards?

Plan for 10-15% waste factor to account for cuts, mistakes, and future repairs. Diagonal installations (45° angle) typically require 15-20% waste due to more angled cuts.

What materials do I need for decking besides boards?

Besides deck boards, you'll need fasteners (screws or hidden fasteners), joist hangers, pressure-treated lumber for framing, flashing, and potentially railing materials depending on your design.

How do I measure my deck for materials?

Measure the length and width of your deck area. For irregular shapes, break them into rectangles and calculate each section separately. Always double-check measurements before ordering materials.

Should I install deck boards at 90° or 45° to the joists?

90° installation is easier, uses less material, and creates less waste. 45° installation looks more decorative but requires more boards, more cuts, and increases waste by 15-20%.

What's the difference between 12", 16", and 24" joist spacing?

Closer joist spacing (12" or 16") provides better support and reduces board sagging, especially important for thinner deck boards. 24" spacing is acceptable for thicker boards but may feel less solid.