Deck Boards Calculator

Frequently Asked Questions About Building Decks

Q1. How many deck boards do I need?

To find how many deck boards you need, divide the deck’s total square footage by the coverage of one board, accounting for the gap between boards. A common 5.5 inch wide board with a 1/4 inch gap effectively covers about 5.75 inches; divide your deck’s length by the board’s effective width to get the number of rows, then multiply by the boards needed per row. Always add about 10% for waste, cuts, and defects. Our Deck Boards Calculator does this automatically from your deck dimensions.

Q2. What decking material should I choose?

Pressure-treated lumber is the most affordable and widely used, holding up outdoors but requiring periodic sealing or staining. Cedar and redwood are naturally rot- and insect-resistant with a beautiful grain, but still need maintenance. Composite and PVC decking cost more upfront but resist rot, fading, and splintering, and need little maintenance beyond cleaning. Tropical hardwoods like ipe are extremely durable and dense but heavy and harder to work. Choose based on your maintenance tolerance, climate, and the look you want.

Q3. What gap should I leave between deck boards?

Leave a gap of about 1/8 to 1/4 inch between deck boards for drainage and airflow. Pressure-treated lumber is often installed tight (with little to no gap) because it shrinks as it dries, opening up the spacing naturally over a few weeks. Kiln-dried hardwoods and composite boards are installed with a consistent gap since they don’t shrink much. Consistent spacing also looks cleaner—many builders use a spacer tool or a nail to keep gaps even along the whole run.

Q4. Should I use hidden fasteners or face screws?

Face-screwing—driving screws down through the top of the board into the joist—is strong, fast, and inexpensive, though the screw heads are visible (countersinking and plugging can hide them). Hidden fastener systems use clips that fit into a groove on the board’s edge, leaving a clean, screw-free surface and consistent spacing, which is popular with composite decking. Hidden fasteners cost more and install slower but give a premium look. Many composite boards are designed specifically for a clip system.

Q5. Which direction should deck boards run?

Deck boards typically run perpendicular to the joists, which is required for structural support. Beyond that, the direction is a design choice: running boards parallel to the longest side or the house often looks best and minimizes the number of boards, while diagonal patterns add visual interest but increase waste (add 15% instead of 10%). The joist spacing underneath—usually 12 to 16 inches on center—must suit your decking material’s span rating, so plan the frame and board direction together.