Deck Material Calculator
Estimate deck boards, joists, screws, and total material cost from your deck dimensions and material grade. Buy the right quantities the first time.
Surface materials only. Footings, ledger flashing, hardware, railings, and stairs typically add 20–30% on top of these estimates. For ground-only base prep, the Gravel Calculator covers footing and pad volume.
Estimate your deck materials
Enter deck dimensions, pick a material grade, and adjust spacing or waste as needed. Board count, joists, screws, and total cost update instantly.
$740
For a 192 sq ft deck using 5.5 in decking boards on 16 in centers.
How to use this calculator
Enter your deck length and width in feet. Select the nominal size of the decking boards you plan to use and the on-center joist spacing. Enter the cost per linear foot of your chosen decking material and the waste percentage you want to include. The calculator returns total decking linear feet, number of joists, deck screws, and material cost.
Tips for success
- Boards run perpendicular to joists. If your deck is 16 ft long and 12 ft wide, the boards span the 16 ft direction and joists sit every 16 in along that length.
- Buy lengths that minimize butt joints. For a 16 ft deck, buy 16 ft boards, not two 8-footers pieced together. Mid-span joints look unfinished and trap water.
- Order 10% extra for rectangles, 15% for angles. Cutoffs from picture-frame borders, mitered corners, and angled decks add up fast.
- Two screws per board per joist. For a 12 ft deck with joists at 16 in centers, that's 10 joists per board and 20 screws per board. A 1 lb box of deck screws has roughly 75–150 screws depending on length.
- Match joist spacing to your boards. 5/4 boards max out at 16 in centers; composite often requires 12 in; 2× decking laid diagonally always needs 12 in centers.
Common mistakes
- Ignoring hidden costs. Ledger flashing, joist hangers, galvanized hardware, and concrete footings add 20–30% on top of the decking and joist budget. Build that into your budget before you start.
- Stretching joist spacing for composite. Composite boards rated for 16 in centers will sag if you go to 24 in. Read the manufacturer's span chart before committing.
- Skipping the permit on a tall deck. Most jurisdictions require one for decks over 30 in off the ground or attached to the house. Unpermitted decks cause problems at sale time.
- Tight waste factor on angled cuts. 10% works for rectangles. For picture-frame borders or 45° angles, plan 15–20%; the offcuts pile up.
- Underbuying screws. A 1,200 sq ft deck needs ~4,200 screws; a 5 lb bucket holds 800–1,400. Round up so a half-finished deck doesn't send you back to the lumber yard.
Practical note
This calculator estimates surface decking, joists, and screws only. You'll still need a ledger board, beams, posts and footings, joist hangers, flashing, railings, and stair materials. Check your local building code for minimum joist size, beam span, post spacing, and footing depth; these vary by snow load and frost line. Pull a permit before starting any deck higher than 30 in off the ground.
What drives the material cost
- Deck area. Material scales directly with square footage. Doubling the deck size roughly doubles the decking, joist, and fastener count.
- Board width. 5.5 in boards cover more ground per piece than 3.5 in boards, so a 5.5 in deck uses ~40% fewer linear feet for the same area.
- Joist spacing. Tighter spacing (12 in on center) uses 33% more joists than 16 in spacing, and bumps fastener count since each board is screwed at every joist.
- Material grade. Pressure-treated pine is cheapest at $2–4 per linear foot. Cedar runs $4–7. Composite costs $5–10 per linear foot and roughly doubles once hidden fasteners are added.
- Waste factor. 10% covers end cuts and occasional defects. Picture-frame borders, mitered corners, and angled decks need 15%+.
FAQ
How many deck boards do I need for a 12x16 deck?
With 5.5 in wide boards (5/4x6 or 2x6), you need about 25 boards running the 16 ft length to cover a 12 ft width. That is roughly 400 linear feet of decking including a 10% waste factor. If you use 3.5 in wide boards instead, plan for about 40 boards and 640 linear feet.
How many screws do I need per square foot of deck?
Roughly 350 deck screws per 100 sq ft of decking using 5.5 in boards at 16 in joist spacing. A 1,200 sq ft deck needs about 4,200 screws. Buy a 5 lb bucket of 2.5 in or 3 in deck screws, which typically contains 800 to 1,400 screws depending on size. Stainless or coated screws cost more but are essential for cedar and ACQ-treated lumber.
How many joists for a 12 ft wide deck at 16 in on center?
A 12 ft span divided by 16 in spacing gives 9 bays plus the two end joists, for a total of 10 joists. For a deck 12 ft wide by 16 ft long, each joist is 12 ft long so you need 120 linear feet of joist lumber. Double the ledger joist if code requires a doubled beam at the house.
Should I use 12 in or 16 in joist spacing?
Use 16 in on center for 5/4 pressure-treated or 2x decking laid perpendicular to joists. Drop to 12 in if you are laying decking diagonally, using composite boards rated for 12 in spacing only, or building a hot tub platform that carries heavy concentrated loads. Tighter spacing adds joists and cost but makes the deck feel more solid underfoot.
How much does it cost to build a deck per square foot?
Material alone runs $15 to $25 per sq ft for pressure-treated, $25 to $40 for cedar, and $35 to $60 for composite. Add another $20 to $40 per sq ft if you hire a contractor. A 12 by 16 pressure-treated deck costs $3,000 to $4,800 in materials, while the same deck in composite costs $6,700 to $11,500.
Do I need a permit to build a deck?
Most jurisdictions require a permit for any deck attached to the house or more than 30 in off the ground. Freestanding ground-level platforms under 200 sq ft are often exempt. Permit fees run $150 to $500 and require an inspection at framing and again at completion. Unpermitted decks can cause problems when selling the home.