Quick Answer
For a standard rectangular deck, you’ll need roughly 1 linear foot of decking board for every (board width + gap) inches of deck width, multiplied by your deck’s length, plus 10–15% extra for cuts and waste. A 12×16 ft deck using 5.5-inch boards typically needs about 215–235 linear feet of decking, which works out to 18–20 boards if you’re buying 12-footers. Use the calculator above to get exact numbers for your dimensions, board width, and pattern.
Deck Material Calculator
Enter your deck size to get boards, linear feet, fasteners, and fascia — in one pass.
Your estimate
This is a planning estimate for material shopping, not a structural or permit document. Board coverage assumes decking runs the length of the deck; flip your length/width entries if your boards will run the other direction. Always round up to the nearest full board when ordering, and check local code before finalizing fastener spacing.
Key Takeaways
- Deck material needs come down to three numbers: square footage, linear footage, and board count — most calculators online only give you one of these.
- Board width and the gap between boards both eat into your coverage — a 1/8-inch gap across a 16-foot-long deck adds up faster than most people expect.
- Diagonal and herringbone patterns don't just look different — they change your waste factor from around 10% to 15–20%.
- Fascia boards are easy to forget until you're back at the lumber yard for a second trip — this calculator includes them.
- Screw count depends on your joist spacing, not just your board count — 16-inch on-center framing needs noticeably more fasteners than 24-inch framing.
Why "Square Footage" Isn't Enough to Order Decking
I get it — the instinct is to measure length times width, get your square footage, and go buy that many square feet of boards. I did the same thing on my first deck job, and I came up almost a full bundle short, because square footage doesn't account for the gaps between boards, the waste from cutting to length, or the fact that lumber yards sell decking by the linear foot in fixed lengths — not by the square foot.
A deck material calculator needs to work backward from your actual board width, your board length options, and your decking pattern to give you a number you can actually hand to a lumber yard clerk. That's the difference between a decking square footage calculator (which most sites give you) and a true deck board calculator that tells you what to put in the cart.
What Goes Into This Calculator
Deck length and width
Your two basic measurements, in feet. If your deck isn't a simple rectangle — an L-shape or wraparound — break it into rectangular sections and run each one through the calculator separately, then add the results together.
Board width
This is your actual milled width, not the nominal size stamped on the lumber. A "1x6" deck board is actually 5.5 inches wide. A "1x4" is 3.5 inches. Composite boards vary by brand, so check the spec sheet — most run close to 5.5 inches as well.
Gap between boards
Pressure-treated lumber is typically installed with a 1/8-inch gap to allow for drainage and seasonal wood movement as the boards dry and shrink. Composite decking often calls for a slightly wider gap — around 3/16 inch — since it doesn't shrink the same way but still needs airflow. Check your manufacturer's install guide; this single number shifts your total board count more than people expect.
Decking pattern
- Straight (perpendicular): the standard layout, boards run across the joists at 90°. Lowest waste.
- Diagonal: boards run at 45° to the joists. Adds roughly 5% more waste from angled cuts.
- Herringbone / picture-frame: the most material-intensive pattern, typically 10%+ extra waste from the additional cuts and border boards.
Board length and waste factor
Decking is sold in fixed lengths — usually 8, 10, 12, 16, or 20 feet. Buying the wrong length means either awkward seams mid-span or paying for length you'll cut off and throw away. The calculator rounds up to whole boards, because lumber yards don't sell partial boards.
Joist spacing and fastener count
Deck screws land where boards cross joists, not randomly along their length. 16-inch on-center framing is the most common residential spacing, but 12-inch o.c. is used for stronger spans or heavier board species, and some lighter setups use 24-inch o.c. This calculator multiplies your board rows by joist crossings to give you a fastener count — not just a rough "a box should cover it" guess.
Fascia boards
Fascia is the trim board that covers the exposed rim joist and end joists — the visible "skirt" around your deck's edge. If your deck is attached to your house on one side, you generally only need fascia on the remaining three sides. Freestanding decks need it on all four.
Wood Deck Cost Calculator: Free Estimate & Cost Guide
Straight vs. Diagonal vs. Herringbone: Material Impact at a Glance
| Pattern | Typical waste factor | Best for | Watch out for |
|---|---|---|---|
| Straight | 8–10% | Most decks, fastest install | Least visually distinctive |
| Diagonal (45°) | 13–15% | Adding visual interest without a big cost jump | More angled end cuts, slightly slower install |
| Herringbone / picture-frame | 18–22% | Statement decks, high-end builds | Significantly more labor and offcuts; border boards need mitered corners |
Common Deck Sizes: Rough Board Counts
These are ballpark figures using 5.5-inch boards, a 1/8-inch gap, straight pattern, and 10% waste — run your exact numbers through the calculator above for anything more specific.
| Deck size | Approx. sq ft | Approx. linear ft needed | Boards (12 ft length) |
|---|---|---|---|
| 10x10 ft | 100 | ~130–140 ft | ~12 boards |
| 12x12 ft | 144 | ~185–200 ft | ~17 boards |
| 12x16 ft | 192 | ~215–235 ft | ~20 boards |
| 16x20 ft | 320 | ~360–390 ft | ~33 boards |
Frequently Asked Questions
How much decking material do I need for a 12x12 deck? For a 12x12 ft deck (144 sq ft) using standard 5.5-inch boards with a 1/8-inch gap and a 10% waste allowance, you'll need roughly 185–200 linear feet of decking, which comes out to about 17 twelve-foot boards.
How do I calculate linear feet of decking from square footage? Divide your deck's width (in inches) by the board width plus the gap between boards, round up to a whole number of rows, then multiply that by your deck's length. That gives you total linear feet before waste — add 10% or more depending on your pattern.
Do I need extra boards for diagonal decking? Yes. Diagonal decking typically adds about 5% more waste than straight decking because of the angled end cuts, and herringbone patterns can add 10% or more.
How many deck screws do I need per board? Each board needs 2 screws at every joist it crosses. For 16-inch on-center joists, that generally works out to roughly 2.5–3 screws per linear foot of decking, though exact counts depend on your joist spacing and board length.
Should I include fascia boards in my material order? Yes — fascia covers the visible rim and end joists around your deck's perimeter, and it's easy to forget until your framing is already exposed. If your deck attaches to the house, you typically only need it on the three open sides.
