How much extra decking material should I buy?

It is standard practice to purchase 10-15% extra decking material. This accounts for waste from cutting, mistakes, and any defective or warped boards you might find in your lumber delivery.

How many screws do I need for my deck?

A general rule of thumb is about 350 screws for every 100 square feet of decking, assuming 6-inch wide boards and 16-inch joist spacing. This calculator provides a rough estimate in pounds, but buying a bulk bucket is usually safer.

What is the gap between deck boards?

Standard spacing is 1/8 to 1/4 inch. This allows for water drainage and wood expansion. If using wet pressure-treated lumber, you can butt them tighter as they will shrink; for composite, follow the manufacturer's specific gap requirements.

Does this calculator include the substructure?

No, this calculator focuses on the decking surface boards and fasteners. It does not calculate materials for footings, posts, beams, or joists, as those depend heavily on local building codes and specific design loads.

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Deck Calculator

Calculate materials and cost for building a deck.

Calculator

Deck Length (feet)

Deck Width (feet)

Deck Board Width (inches)

Deck Board Length (feet)

Price per Board ($)

Results

Total Estimated Cost

$0.00

0 Boards Needed

Reviewed by Mark Johnson, Licensed Contractor | Last Updated: November 2025

Planning Your Deck Build

A well-planned deck adds significant value and enjoyment to your home. Accurate material estimation is the first step to a successful project. This calculator helps you determine the surface decking and fasteners needed, including a standard waste factor.

💡 Pro Tip: The 10% Rule

"Always buy at least 10-15% more lumber than the exact square footage requires. You will inevitably have bad ends to trim off, warped boards you can't use, or mistakes in cutting. It's cheaper to buy extra now than to stop work and drive back to the store."

Common Mistakes to Avoid

Ignoring Board Gaps: Deck boards need space (usually 1/8") to drain water. If you jam them tight, water will pool and rot the wood faster.
Forgetting Railing Posts: If your railing posts are inside the rim joist, you'll need to notch deck boards around them, which takes time and extra material.
Using Interior Screws: Never use drywall screws or non-galvanized fasteners. They will rust and snap within a year. Use polymer-coated or stainless steel deck screws.

Frequently Asked Questions

Pressure-Treated vs. Composite?

Pressure-treated wood is cheaper upfront but requires annual staining/sealing. Composite is 2-3x more expensive but requires almost no maintenance and lasts 25+ years.

How do I calculate concrete for footings?

Footing size depends on your soil type and deck load. Check out our Concrete Calculator to estimate bags needed for your post holes.

What length boards should I buy?

Try to buy boards that match your deck length to avoid butt joints (seams). If your deck is 12' wide, buy 12' boards. It looks cleaner and lasts longer.