Deck boards are sold in fixed lengths, so the number you need depends on how your board length divides into your deck width — not just on square footage. This calculator accounts for board coverage including the gap, joist spacing, and fastener counts.
Pricing a specific brand? See Trex, TimberTech, or composite decking costs.
Deck Board Calculator
Enter deck dimensions, board size, and joist spacing. Results give board counts and fasteners.
The Deck Board Formula
Rows = Deck Width ft ÷ Board Coverage ft
Boards = Rows × (Deck Length ft ÷ Board Length ft), rounded up
Board Coverage = (Board Width in + Gap in) ÷ 12
A nominal 5/4 × 6 deck board is actually 5.5 inches wide, and a standard installation gap is 1/8 to 1/4 inch. That means each board covers about 5.75 inches, or 0.479 feet — not the 6 inches its name implies. Ignoring this understates the board count by roughly 4%.
Worked example: A 16 × 12 ft deck with 5/4 × 6 boards running the 16 ft direction. Rows across the 12 ft width: 12 ÷ 0.479 = 25.1 → 26 rows. Each row needs one 16 ft board. That is 26 boards, plus 10% waste = 29 boards. At $28 each, $812 in decking.
Deck Board Coverage and Counts
Coverage includes a 1/4 inch installation gap. Board counts are per 100 square feet before waste.
| Board Size | Actual Width | Coverage w/ Gap | LF per 100 Sq Ft | 16 ft Boards per 100 Sq Ft |
|---|---|---|---|---|
| 5/4 × 4 | 3-1/2 in | 3-3/4 in | 320 | 20 |
| 5/4 × 6 | 5-1/2 in | 5-3/4 in | 209 | 13 |
| 2 × 4 | 3-1/2 in | 3-3/4 in | 320 | 20 |
| 2 × 6 | 5-1/2 in | 5-3/4 in | 209 | 13 |
| 2 × 8 | 7-1/4 in | 7-1/2 in | 160 | 10 |
| Composite 1 × 6 | 5-1/2 in | 5-3/4 in | 209 | 13 |
Composite decking requires wider gaps than wood in hot climates because it expands more with temperature. Follow the manufacturer's spacing spec — typically 1/8 inch for end-to-end and 1/4 inch side-to-side.
Deck Framing Requirements
Joist spacing is dictated by decking type and installation direction, and it drives your framing lumber order.
| Decking Type | Max Joist Spacing | Diagonal Install | Notes |
|---|---|---|---|
| 5/4 wood decking | 16 in OC | 12 in OC | Most common residential build |
| 2x wood decking | 24 in OC | 16 in OC | Thicker, spans further |
| Capped composite | 16 in OC | 12 in OC | Check manufacturer spec |
| PVC decking | 16 in OC | 12 in OC | More flexible than composite |
| Hardwood (ipe, cumaru) | 16 in OC | 12 in OC | Very stiff but heavy |
| Aluminum decking | 24 in OC | 16 in OC | Longest spans available |
Joists at 16 inches on center means a 12 ft wide deck needs 10 joists, calculated as 12 ft ÷ 1.33 ft + 1. Always add one for the closing joist, and check whether your span requires doubled rim joists.
What a Finished Deck Costs
Deck boards are only one line item. For context on the whole project, ConcreteNetwork puts a wood deck at $15 to $40 per square foot installed, driven by material choice, labour, and design complexity — against $5 to $18 per square foot for a concrete patio of the same footprint.
| Surface | Installed per Sq Ft | On a 12×16 ft (192 sq ft) | Note |
|---|---|---|---|
| Wood deck (any species) | $15–$40 | $2,880–$7,680 | Sourced figure; spans PT through hardwood |
| Concrete patio | $5–$18 | $960–$3,456 | Plain $5–8, elaborate $18+ |
| Paver patio | $4–$20 | $768–$3,840 | Basic $4–6, elaborate $7–20 |
Source: ConcreteNetwork.com concrete patio cost guide (updated January 2026), which quotes the wood deck, concrete patio, and paver ranges above for comparison. A raised deck with railings, stairs, and footings sits at the upper end; a low ground-level deck sits near the bottom.
Fasteners and Hardware per 100 Square Feet
| Item | Quantity | Cost | Notes |
|---|---|---|---|
| Deck screws (face screwed) | 350–400 | $25–$45 | 2 per board per joist |
| Hidden fastener clips | 180–220 | $90–$180 | Composite grooved boards |
| Joist hangers | 10–14 | $25–$50 | One per joist end |
| Structural screws for ledger | 20–30 | $30–$60 | Per code, not lag bolts alone |
| Joist tape / flashing | 100 LF | $40–$90 | Often doubles framing life |
| Post base brackets | 2–6 | $30–$90 | Depends on post count |
Hidden fasteners cost three to four times more than face screws but leave no visible screw heads. They also make individual board replacement much harder later, since the clips lock adjacent boards together.
Common Deck Board Mistakes
Using Nominal Width Instead of Actual Coverage
A 5/4 × 6 board is 5.5 inches wide, not 6, and with a quarter-inch gap it covers 5.75 inches. Calculating rows on a 6-inch assumption understates the board count by about 4% — on a large deck that is several boards short, and the replacements may come from a different production lot with visible color variation.
Forgetting That Board Length Must Divide the Deck
Square footage alone does not determine board count. A 17 ft deck run using 16 ft boards needs two boards per row with a butt joint, effectively wasting 15 feet per row. Designing the deck to a dimension that matches available board lengths, or accepting a deliberate picture-frame border, avoids substantial waste.
Spacing Joists at 24 Inches Under 5/4 Decking
Five-quarter decking is rated for 16 inches on center. At 24 inches it flexes underfoot and will hold a permanent sag between joists within a few seasons. Only 2x decking and some aluminum systems are rated for 24-inch spacing, and even then only for straight rather than diagonal installation.
Skipping Joist Tape
Water sits in the seam between deck board and joist top, and that trapped moisture is what rots framing long before the decking itself fails. Self-adhesive joist tape costs $40–$90 per 100 linear feet and commonly doubles framing life. It is the highest-return hundred dollars on the entire project and takes an afternoon to apply.
About these price ranges
Pricing varies widely by region, season, project size, and site conditions. Treat every figure on this page as a planning estimate for budgeting only — not as a quote. Coastal metro markets commonly run 20–40% above national ranges while rural inland markets can fall 10–20% below. Always collect at least three written quotes from local contractors before committing to a budget.
Sourced figures: ConcreteNetwork.com patio cost guide (installed wood deck, concrete patio, and paver ranges).
Unsourced estimates: Per-board prices and fastener / hardware line items. These are informed planning figures rather than data drawn from a published price index, and they carry a correspondingly wider margin of error.