How Many Deck Boards Do I Need for My Deck?

Building a deck? Running out of boards mid-project means an extra trip to the lumber yard, or worse, discovering your batch is sold out and the new boards don’t match. This guide shows you exactly how many deck boards you need.

The Quick Answer

For a 12×16 foot deck (192 sq ft) using 5.5-inch actual width boards at 16-inch joist spacing:

• Base boards needed: 35 boards (8-foot length)
• With 10% waste factor: 39 boards
• Cost estimate: $195–$390 (at $5–$10 per board)

For a 10×12 foot deck (120 sq ft): 24 boards (with waste).

For a 14×20 foot deck (280 sq ft): 57 boards (with waste).

The Formula

Deck board quantity depends on coverage area, board width, and waste:

Boards Needed = (Deck Area ÷ Board Coverage) × (1 + Waste Factor)

Step-by-Step Calculation

1. Calculate deck area: Length × Width (in feet)
2. Determine board coverage: Board width (actual, not nominal) ÷ 12 × Board length
3. Divide: Deck area ÷ Board coverage = base board count
4. Add waste: Multiply by 1.10 (for 10% waste) or 1.15 (for 15%)

Example: 12×16 Deck with 5.5” Wide Boards (8-foot length)

1. Deck area = 12 × 16 = 192 sq ft
2. Board coverage = (5.5 ÷ 12) × 8 = 3.67 sq ft per board
3. Base count = 192 ÷ 3.67 = 52.3 boards
4. With 10% waste = 52.3 × 1.10 = 58 boards

Wait. That’s for laying boards the 8-foot direction. If you run boards along the 16-foot direction, you’ll need 16-foot boards or splice 8-footers.

Corrected for Board Layout Direction

If running boards perpendicular to the 16-foot side (across the 12-foot width):

• Board coverage per 8-foot board = 5.5” × 8 ft = 3.67 sq ft
• Number of boards = 192 ÷ 3.67 = 52.3 → 58 boards (with waste)

If running boards parallel to the 16-foot side (across the 12-foot width):

• You need 16-foot boards, or splice two 8-footers
• Number of boards = (12 ft ÷ 5.5”) × 1.10 = (12 ÷ 0.458) × 1.10 = 29 boards

Most builders run boards perpendicular to the longest span for strength.

Deck Size Reference Chart

Deck Size	Square Feet	5.5” Boards (8ft)	5.5” Boards (12ft)	6” Boards (8ft)
Small (8×10)	80 sq ft	25 boards	17 boards	23 boards
Medium (10×12)	120 sq ft	37 boards	25 boards	34 boards
Standard (12×16)	192 sq ft	58 boards	39 boards	53 boards
Large (14×20)	280 sq ft	85 boards	57 boards	78 boards
XL (16×24)	384 sq ft	116 boards	78 boards	107 boards
Master (20×30)	600 sq ft	181 boards	121 boards	167 boards

All quantities include 10% waste factor and assume boards run the short direction

Board Width Options

Deck boards come in nominal sizes, but actual dimensions are smaller after planing.

5.5-Inch Actual Width (Nominal 6-inch)

Actual coverage: 5.5 inches per board

Pros:

• Industry standard with widest availability
• Balances cost and coverage
• Works with all fastening systems

Cons:

• More boards needed than wider options
• More seams/gaps to maintain

Best for: Most residential decks, budget-conscious builds

6-Inch Actual Width (Nominal 6-inch premium milled)

Actual coverage: 6 inches per board

Pros:

• Fewer boards = faster installation
• Fewer seams = cleaner look
• Slightly lower labor cost

Cons:

• Limited availability (premium product)
• Higher cost per board
• Fewer fastener options

Best for: High-end decks, modern designs

5.25-Inch Actual Width (Composite/PVC)

Many composite brands use 5.25” actual width.

Pros:

• No rot or splinters
• Low maintenance (no staining)
• 25-year warranties

Cons:

• 2-3x material cost vs. wood
• Heat retention (uncomfortable barefoot)
• Fades over time despite claims

Best for: Low-maintenance decks, coastal areas

Material Comparison

Pressure-Treated Pine

Cost: $5–$8 per 8-foot board

Lifespan: 15–20 years (with proper maintenance)

Maintenance: Stain/seal every 2–3 years

Pros:

• Cheapest upfront cost
• Readily available
• Easy to cut and work with

Cons:

• Requires regular maintenance
• Prone to warping, cupping, splitting
• Chemical treatment concerns (use gloves during cutting)

Best for: Budget builds, DIY-friendly projects

Cedar

Cost: $12–$18 per 8-foot board

Lifespan: 20–30 years

Maintenance: Seal annually to preserve color (or let it gray naturally)

Pros:

• Natural rot resistance
• Beautiful grain and color
• Pleasant aroma

Cons:

• 2x cost of pressure-treated
• Still requires sealing for color
• Softer wood = dents more easily

Best for: Premium wood aesthetic, natural appeal

Composite (Trex, TimberTech, etc.)

Cost: $15–$25 per 12-foot board

Lifespan: 25–50 years

Maintenance: Wash with soap and water annually

Pros:

• No staining, sealing, or painting
• Resists rot, insects, UV
• Splinter-free

Cons:

• Highest upfront cost
• Can’t be sanded or refinished
• Hot to the touch in direct sun

Best for: Long-term low-maintenance decks

Joist Spacing Requirements

Joist spacing affects board strength and spacing requirements.

12-Inch On-Center (OC)

When required:

• Deck boards thinner than 1 inch (rare)
• Composite boards (check manufacturer specs)
• High-traffic commercial decks

Material impact: No change. Same coverage, just more joists needed

16-Inch On-Center (OC)

When required:

• Standard for 5/4 or 2× lumber (most residential decks)
• Code compliant for most regions

Material impact: Standard calculation applies

Most common residential choice

24-Inch On-Center (OC)

When allowed:

• 2× lumber running perpendicular to joists
• Low-traffic decks
• Check local codes first

Material impact: Board count unchanged, but risk of bounce/flex

Pros: Fewer joists = lower framing cost

Cons: Deck feels bouncy, boards can sag between joists

Recommendation: Stick with 16” OC for residential decks.

Calculating Joists and Screws

Joist Count Formula

Joists Needed = (Deck Width ÷ Joist Spacing) + 1

For a 12-foot wide deck at 16-inch OC:

• (12 ft × 12 inches) ÷ 16 = 9 spaces
• 9 spaces + 1 = 10 joists

Screw Count Formula

Screws per Board = 2 screws per joist × Number of joists board crosses

For a 12×16 deck:

• Each 8-foot board crosses 7 joists (12 ft ÷ 16” OC)
• Screws per board = 2 × 7 = 14 screws
• Total boards = 58
• Total screws = 58 × 14 = 812 screws

Buy in bulk: 5-pound box of deck screws = approximately 1000 screws ($25–$40).

Pro Tips from Deck Builders

1. Always Buy Extra Boards

Lumber yards sell from the same batch, but they rotate stock. If you run short and come back a week later, the new batch may have different color or grain.

Rule: Add 15% waste (not 10%) if you’re new to deck building because mistakes happen.

2. Crown the Boards

Every board has a slight curve (the “crown”). When installing:

1. Sight down the edge of each board
2. Identify the high point of the curve
3. Install with crown UP

This prevents sagging and water pooling.

3. Butt Joints on Joists

If splicing two boards end-to-end:

• Both ends must land on the same joist
• Leave 1/8” gap between ends for expansion
• Stagger joints. Don’t align across adjacent boards (looks like a fault line)

4. Gap Spacing Matters

Wood expands in humidity, shrinks when dry.

Climate	Gap Spacing
Dry regions (AZ, NM)	1/8”
Moderate humidity	3/16”
High humidity (FL, Gulf)	1/4”
Green/wet lumber	1/16” (will expand)

Use 16d nails as spacers (exactly 1/8” thick).

5. Hidden Fastener Systems

Systems like Tiger Claw, Camo, EB-TY hide screws from view.

Pros:

• Clean top surface (no screw heads)
• Faster installation (clip-in systems)
• Consistent gap spacing

Cons:

• Add $0.50 to $1 per sq ft
• Require grooved deck boards or pre-drilling
• Can’t be used on end boards (still need face screws)

Material impact: Add 5% to board count for end cuts and starter/finish boards.

6. Order Joists and Beams First

You can’t lay deck boards without a frame. Order framing lumber first and verify your layout before finalizing board count.

If you discover you need to adjust deck size by 6 inches, your board count changes.

Common Deck Building Mistakes

1. Not Accounting for Board Overlap

Scenario: You calculate for a 12-foot deck, buy exactly enough boards, then realize boards overhang the frame by 1 inch on each side.

Result: You’re 2% short on boards.

Fix: Measure the final deck surface, not the frame, and account for overhang (typically 1–1.5 inches per side).

2. Ordering Wrong Board Lengths

Wrong: Ordering all 8-foot boards for a 10-foot wide deck.

Result: Every board needs a splice, doubling joist touch points and wasting time.

Right: Order 12-foot boards for 10-foot spans. You’ll have 2 feet of scrap per board (use for stairs or borders).

3. Ignoring Local Code Requirements

Many regions require:

• Maximum joist spacing (16” OC for residential)
• Minimum board thickness (5/4 lumber = 1 inch actual)
• Fastener type (galvanized or stainless in coastal areas)

Fix: Pull permits and ask your building inspector before ordering materials.

4. Using Drywall Screws

Never use drywall screws on decks because they rust in 6 months.

Required: Exterior-grade deck screws (coated or stainless steel)

Cost: $8–$12 per pound vs. $4 for drywall screws. Worth every penny.

5. Skipping Moisture Barriers

If your deck is over living space, you need waterproofing between joists and boards.

Options:

• Under-deck drainage systems (Trex RainEscape, TimberTech DrySpace)
• Joist tape (butyl rubber tape on top of each joist)

Material impact: Joist tape adds $0.20 per linear foot of joist. For a 12×16 deck with 10 joists (each 16 ft long), that’s 160 linear feet = $32 for joist tape.

Hidden Fastener Systems Impact

If using hidden fasteners, adjust your board count:

Additional boards needed:

• Starter board (1 board)
• Finish board (1 board)
• Damaged clip holes (2 to 3 boards as buffer)

Total: Add 5% to final board count for hidden fastener systems.

For a 12×16 deck (58 boards), that’s 3 extra boards = 61 boards total.

Cost Breakdown Example

For a 12×16 deck (192 sq ft) with pressure-treated 5.5” boards at $6 each:

Item	Quantity	Unit Cost	Total
Deck boards (8 ft)	58 boards	$6	$348
Joists (2×8, 16 ft)	10 joists	$18	$180
Beams (2×10, 16 ft)	2 beams	$28	$56
Deck screws (5 lb box)	1 box	$35	$35
Joist hangers	20 hangers	$2	$40
Post anchors	6 anchors	$8	$48
Concrete (60 lb bags)	12 bags	$6	$72
Stain/sealer (5 gal)	1 bucket	$120	$120
Total Materials			$899

Add 10% contingency for errors, tool rental, fastener overruns: $990 total.

Labor (if hiring): $8 to $15 per sq ft = $1,536 to $2,880 additional.

Using the Deck Calculator

For complex deck shapes (L-shaped, multi-level, angled corners), use our deck calculator to:

• Input exact dimensions in feet and inches
• Select board width (5.5”, 6”, or custom)
• Choose joist spacing (12”, 16”, or 24”)
• Get instant board counts and material lists
• Calculate joist, beam, and fastener quantities
• Estimate total project cost

The calculator automatically applies appropriate waste factors and rounds to bundle quantities.

Final Checklist

Before you buy:

• Measured deck length and width (in feet)
• Determined board layout direction (perpendicular to long side or short side)
• Selected board width (5.5” or 6” actual)
• Chose board length (8 ft, 10 ft, 12 ft, or 16 ft)
• Selected material type (pressure-treated, cedar, or composite)
• Verified joist spacing requirement (12”, 16”, or 24” OC)
• Applied appropriate waste factor (10–15%)
• Rounded up to nearest full board
• Added 5–10 extra boards for future repairs
• Calculated joists, beams, and fasteners
• Checked local building codes and permit requirements

Frequently Asked Questions

How many deck boards do I need for a 12x16 deck?

For a 12x16 deck (192 square feet) using standard 5.5-inch wide boards (8-foot length), you need 58 boards with 10% waste included. This assumes boards run perpendicular to the 16-foot side. If using 12-foot boards running the opposite direction, you need 39 boards. Always add 5-10 extra boards as a repair reserve for future damage.

Should I use 5.5-inch or 6-inch deck boards?

5.5-inch actual width boards (nominal 6-inch) are the industry standard and offer the best balance of cost, availability, and performance. True 6-inch boards are premium-milled products with slightly better coverage (fewer boards needed) but cost more and have limited availability. For most residential decks, stick with standard 5.5-inch boards.

How much waste should I add when ordering deck boards?

Add 10% waste for experienced builders using simple rectangular decks with standard board patterns. Increase to 15% if you’re a DIYer, have an irregular deck shape, or plan diagonal or herringbone patterns. The waste accounts for miscuts, damaged boards, end trims, and future repairs. It’s cheaper to have extras than to run short mid-project.

Do I need to buy the same batch of lumber?

Yes because lumber color and grain vary between production batches even in the same species. The batch number is stamped on the lumber bundle. Order all deck boards at once from the same batch to ensure consistent appearance. If you run short and reorder from a different batch weeks later, the color mismatch will be obvious, especially with cedar.

What joist spacing should I use for deck boards?

Use 16-inch on-center (OC) joist spacing for standard 5/4 or 2× deck boards on residential decks. This is code-compliant in most regions and provides a solid, bounce-free surface. Composite deck boards often require 12-inch OC spacing (check manufacturer specifications). Avoid 24-inch spacing unless using 2× boards because it creates a bouncy, unstable deck.

Use our deck calculator to eliminate guesswork and ensure you order exactly what you need. No shortages, no expensive overruns.