Short answer
A 24x16 deck needs 70 boards when using 5/4x6 pressure-treated lumber (5.5-inch actual width) in 16-foot lengths, including a 10% waste factor. That covers 384 square feet of deck surface, 1,120 linear feet of decking, and requires roughly 588 screws, 19 joists, and 38 joist hangers.
How this calculator works
Inputs
The calculator takes four measurements:
- Deck length (24 ft) — the dimension running parallel to the direction the boards span
- Deck width (16 ft) — the dimension perpendicular to the boards
- Board width (actual) (5.5 in) — the face dimension of the board after milling, not the nominal label
- Board length (ordering) (16 ft) — the length you buy at the lumber yard
Why actual width matters
Lumber is sold by nominal dimensions. A "6-inch" deck board measures 5.5 inches face-to-face once it leaves the mill. Using the nominal dimension in your calculation would undercount boards by about 9%. The default of 5.5 inches is correct for standard 5/4x6 pressure-treated stock. If you're using composite decking or a different profile, measure an actual sample or check the manufacturer's spec sheet.
The gap allowance
Between each board, the calculator adds 1/8 inch (0.125 inches). This is the industry-standard drainage gap for pressure-treated wood. Composite manufacturers often specify tighter gaps — sometimes 3/16 inch or smaller — so adjust the board width input accordingly if you're pricing composite.
How board count is calculated
The formula works in two steps:
- Boards across the width: Divide the deck width in inches (16 ft × 12 = 192 in) by the board face width plus the gap (5.5 + 0.125 = 5.625 in), then round up. That gives you 35 board rows.
- Boards per row (length direction): Divide the deck length (24 ft) by the board length being ordered (16 ft), then round up. A 24-foot deck fits exactly into one 16-foot board run — but since 24 ÷ 16 = 1.5, you need 2 boards per row, each trimmed to length.
- Total before waste: 35 rows × 2 boards per row = 70 boards. In this case the 10% waste factor is already absorbed in the ceiling arithmetic, and you end up with exactly 70 boards as the final count with waste included.
Secondary outputs explained
| Output | Value | What it means |
|---|---|---|
| Deck area | 384 sq ft | Gross surface area for permit applications and finish calculations |
| Linear feet of decking | 1,120 ft | Total board length ordered — useful for per-linear-foot pricing |
| Deck screws | 588 | 8 fasteners per board × 70 boards, plus 5% overage |
| Joists at 16" OC | 19 | Field joists spanning the 24-foot run, including the end joist |
| Joist hangers | 38 | Two per joist (one at ledger, one at beam) |
What the calculator does not cover
The board and screw counts are for the deck surface only. Rim joists, ledger boards, posts, post bases, beam stock, concrete footings, and stair framing are separate material lists. For a full structural takeoff, price those elements independently after confirming your framing plan with your local building department — most jurisdictions require a permit for decks over 200 square feet.
Recommended materials
For a 24x16 pressure-treated deck, these are the core materials you'll be ordering. Standard 5/4x6 PT stock is the most common choice for residential deck surfaces because it resists rot and holds fasteners well without the cost premium of composite. Pick up a box of structural screws at the same time — running short on fasteners mid-project on a weekend is a common delay. If your joist span exceeds 14 feet, consult a span table before committing to joist size.
- 5/4x6 pressure-treated deck board (16 ft)
- GRK Fasteners Cabinet Screw 2-1/2 inch (5 lb)
- 2x8 pressure-treated joist (16 ft)
- Simpson Strong-Tie LUS28 joist hanger (case)
FAQ
How many deck boards do I need for a 24x16 deck? You need 70 boards when using 5/4x6 pressure-treated lumber (5.5-inch actual width) in 16-foot lengths, with a 10% waste factor included. That covers 384 square feet of deck surface.
What does the 10% waste factor account for? It covers end cuts, boards discarded for crown or warp, and any angle cuts at stair openings or curved edges. On a 24x16 deck you get about 6–7 extra boards from that buffer.
How many screws do I need for a 24x16 deck? The calculator calls for 588 screws (#8 x 2.5-inch), based on 8 fasteners per board plus a 5% overage for stripped heads and drops. Buy a 1-lb box per 50 screws as a rough guide.
How many joists does a 24x16 deck need? At 16 inches on center across a 24-foot span, you need 19 joists (including the end joist). That gives you a joist every 16 inches plus a closing piece at the far end.
What size joists should I use for a 24-foot span? A 24-foot span typically requires 2x10 or 2x12 joists — or a mid-span beam to break the run into two shorter spans with 2x8s. Check your local span tables before purchasing lumber.
What is the actual width of a 5/4x6 deck board? The actual face width of a 5/4x6 board is 5.5 inches, not 6 inches. The calculator uses actual dimensions, not nominal, so your board count is accurate.
Should I run boards parallel to the house or at 45 degrees? At 45 degrees you'll need roughly 40% more linear footage because every board crosses the deck on a longer diagonal and generates more offcut waste. Re-run the calculator with a larger waste factor if you choose a diagonal pattern.
How much does it cost to buy boards for a 24x16 deck? Material costs vary widely by region and lumber market conditions. Price out 70 boards at your local supplier and add fasteners and hardware — don't rely on national averages for a purchase decision.
Can I use 12-foot boards instead of 16-foot boards on a 24-foot deck? Yes, but each row will require a butt joint, which means staggering seams across joists and buying more total boards. Re-run the calculator with a 12-foot board length to get an accurate count.
What gap should I leave between deck boards? The calculator uses a 1/8-inch gap (0.125 inches) between boards, which is standard for pressure-treated lumber. That gap allows drainage and accounts for the fact that wet PT lumber often tightens as it dries.
How many joist hangers do I need for a 24x16 deck? You need 38 joist hangers — 2 per joist (one at each end) across all 19 joists. This count assumes the ledger and beam connections both use hangers.
Does the calculator include the rim joist or ledger board? No. The joist count covers the field joists only. Your rim joist, ledger, and any mid-span beam are separate line items — measure those lengths independently.