How Many Deck Boards for a 10x12 Deck? Full Materials Takeoff

A 10x12 deck is one of the most common DIY sizes - big enough for a table and chairs, small enough to build in a weekend. Materials-wise, you need about 25 deck boards (5/4x6, 12 ft long), 9 joists (2x8x10 ft), 6 concrete footings, 4 posts and 200 deck screws. Here is the full takeoff.

How many deck boards do I need?

A 10 ft x 12 ft deck has 120 sq ft of surface. With standard 5/4x6 deck boards (5.5 inch actual width plus 3/16 inch gap = 5.69 inch module), running the boards along the 12 ft direction:

• Rows of boards: 120 inches (10 ft width) ÷ 5.69 inches = 22 rows
• Boards per row: 12 ft board length covers the full row with no joints
• Total boards: 22 boards
• With 10% waste: 25 boards (rounded up)

Run your specific deck dimensions through the deck board calculator - it handles different board widths, gaps and pattern waste factors.

How many joists do I need?

Joists run perpendicular to the deck boards (so across the 10 ft direction in this example). At 16 inch on-center spacing:

• Joist count: (12 ft × 12 inches per ft) ÷ 16 inch spacing + 1 starter = 10 joists
• Joist length: 10 ft each (matching the deck width)
• Joist size: 2x8 pressure-treated is standard for a 10 ft span; 2x10 if you want stiffer floor feel

Pressure-treated Southern Pine 2x8 at 16 in OC handles 11 ft 11 in for deck loads - comfortably more than the 10 ft span needed here. If you go 24 in OC instead of 16, you save 3-4 joists but the deck feels bouncier underfoot.

How many footings and posts?

Footing layout depends on whether the deck is attached to the house (ledger board) or free-standing:

House-attached deck (most common):

• Ledger board on the house wall (no footings needed - bolts into the rim joist)
• Beam at the outer edge (12 ft from the house)
• 3-4 footings under the outer beam at 4-6 ft spacing
• 3-4 corresponding 6x6 posts

Free-standing deck: double the footing count - one beam on the house side and one beam on the outer side, each on its own row of footings.

For the standard 4 footings at 12 inch diameter, 36 inches deep with 6x6 posts: each footing needs about 1.85 cubic feet of concrete after post displacement = 7.4 cubic feet total = 13 bags of 80lb concrete with 10% waste. Use the deck footing calculator for exact bag counts based on your frost line.

How many deck screws?

Two screws per joist per board crossing. With 22 deck boards and 10 joists:

• 22 boards × 10 joists × 2 screws = 440 screws total
• 1 lb of 2.5 inch deck screws holds about 100-130 screws
• So you need about 4-5 lbs of deck screws total

Use coated or stainless deck screws - never drywall screws (they corrode within months outdoors). For composite decking, use the manufacturer-specified hidden fastener clips or color-matched screws.

What about the railing?

A 10x12 deck attached to the house typically has railing on 3 sides (house side has the wall):

• Railing perimeter: 10 + 12 + 10 = 32 linear feet
• Posts at 6 ft spacing: 6 posts (corners + midspan)
• Balusters at 4.5 in OC (IRC compliant): 32 ft × 12 ÷ 4.5 = 85 balusters
• Top + bottom rail: 64 linear feet of 2x4

Stairs add another 6-12 balusters, 1-2 rails and 2 posts depending on the stair width. Use the deck railing calculator for the full railing takeoff.

What is the total materials cost?

Rough 2026 US pricing for a basic pressure-treated 10x12 deck (lumber only, no railing):

• Deck boards (25 × 5/4x6 × 12 ft PT): $250-400
• Joists (10 × 2x8 × 10 ft PT): $150-220
• Beam (2 × 2x10 × 12 ft PT doubled): $60-90
• Posts (4 × 6x6 × 10 ft PT): $200-300
• Concrete (13 × 80lb bags): $80-120
• Hardware (joist hangers, post anchors, screws): $150-250

Total framing materials: $890-1,380. Add another $400-800 for railing and stairs. Composite decking instead of pressure-treated triples the deck board cost but lasts 25+ years vs 10-15 for wood.

What if my deck is a different size?

The math scales linearly. A 12x14 deck has 168 sq ft (40% bigger than 10x12) and needs about 40% more boards, joists and footings. A 16x16 deck (256 sq ft) doubles the materials count. Run your exact dimensions through the deck board calculator and deck footing calculator to get the exact takeoff.

Should I get a permit?

Yes for most decks over 30 inches off the ground or larger than 200 sq ft (varies by jurisdiction). Check your local building department. A 10x12 ground-level deck (platform 12 inches or less above grade) often does not need a permit. Attached decks almost always need a permit because the ledger board attachment is a critical structural connection - and getting it wrong is the #1 cause of deck collapses.