Deck Board & Joist Calculator
Wondering how many deck boards you need? This free deck materials estimator sizes up your deck boards, joists, rim boards, and fasteners in seconds. Just enter your deck's dimensions, board width, gap, board length, and joist spacing — every result recalculates instantly as you type.
Enter your numbers
Boards run along the deck length; joists run across the width, spaced along the length.
Your results
| Boards across width | — |
|---|---|
| Deck board linear feet (incl. 10% waste) | — |
| Joists (each 12 ft) | — |
| Joist linear feet | — |
| Rim boards (perimeter) | — |
| Deck screws (estimate) | — |
Screw count assumes 2 screws per board per joist crossing. Hidden fastener clips are a cleaner alternative — check compatibility with your board type. Not included: posts, beams, ledger board, joist hangers, or concrete footings.
How to use this calculator
Measure your deck's length and width in feet and enter them first. Then enter the actual width of your deck boards in inches (a nominal "2×6" is usually 5.5 in) and the gap you plan between boards — 1/4 in is the typical choice for pressure-treated lumber. Choose the board length your lumber yard stocks and your joist spacing. Everything updates instantly as you change any value.
How it works
Deck boards: boards needed across the width = deck width ÷ (board width + gap), rounded up. Total board footage = boards across × deck length × 1.10, adding 10% for cuts and waste. Boards to buy = total footage ÷ board length, rounded up.
Joists: joists = (deck length ÷ joist spacing) + 1 — the first joist starts at the ledger and each one runs the full deck width. Total joist linear feet = joist count × deck width.
Rim boards: these frame the perimeter, so footage = 2 × (length + width), with 5% waste added before rounding up to whole boards.
Fasteners (estimate): screws = boards across × joist count × 2, since each board gets two screws where it crosses each joist. Five-pound box quantities assume roughly 1,500 screws per box — treat this as a rough estimate and confirm with the box label. Assumptions: boards run lengthwise along the deck; joists run across the width; posts, beams, ledger, hangers, and footings are not included.
Frequently asked questions
How many deck boards do I need for a 16x12 deck?
With standard 5.5-inch boards, 1/4-inch gaps, and 16-ft board stock, a 16×12 deck needs 26 boards across the width — 457.6 linear feet including 10% waste, so you should buy 29 sixteen-foot boards. Enter your exact numbers above for any other deck size.
What joist spacing should I use for a deck?
16 inches on center is the standard for most residential decks with perpendicular decking. Use 12 inches on center for diagonal decking patterns or a stiffer feel underfoot. 24 inches on center is generally only acceptable for very light-duty or low decks — always check your local building code before finalizing.
How big should the gap between deck boards be?
A 1/4-inch gap is the common default for pressure-treated lumber, which shrinks as it dries. Composite boards typically specify 1/8- to 3/16-inch gaps — follow the manufacturer's instructions, since composite boards don't shrink the same way wood does.
Should I use screws or hidden fasteners?
Face screws are the cheapest and simplest option — this calculator estimates two screws per board at each joist crossing. Hidden fastener clips cost more but leave a clean, screw-free surface and can speed up installation. Just confirm the clip system is compatible with your board type and thickness first.
Do I need a permit to build a deck?
In most areas, yes: attached decks and decks above a certain height (often 30 inches) usually require a permit and inspections. A few jurisdictions exempt small ground-level decks. Check with your local building department before buying materials.