Deck Material Calculator
Enter your deck's length and width to get a complete material takeoff — decking boards, joists, screws, footing concrete and a planning cost estimate — in one step, with the formula shown underneath.
Result
- Deck area192sq ft
- Decking boards29boards
- Joists10joists
- Joist linear feet120lin ft
- Rim + ledger framing56lin ft
- Deck screws744screws
- Concrete (if pier footings)20.7cu ft
- 50 lb concrete bags56bags
- Est. material cost (PT)1222USD
- Area (metric)17.8m²
How it works
boards = area ÷ coverage × waste | joists = (width×12 ÷ spacing) + 1 | screws = rows × joists × 2
- Area = 16 × 12 = 192 sq ft
- Coverage per 16 ft board (5.5" + 0.125" gap) = 7.5 sq ft
- Boards = ceil(25.6 × 1.1) = 29
- Rows across 12 ft = 26
- Joists = ceil(144 ÷ 16) + 1 = 10
- Joist linear feet = 10 × 12 = 120 ft
- Rim + ledger = 2 × (16 + 12) = 56 ft
- Screws = 26 rows × 13 joists × 2 × waste = 744
- Footings = 6 × 3.14 cu ft = 20.73 cu ft → 56 bags of 50 lb
- Planning cost (PT lumber, no labor) = $864 decking + $238 framing + $120 hardware = $1222
How the deck material calculator works
The calculator runs four estimates from a single set of dimensions. Decking boards come from area divided by coverage per board (face width plus a 1/8 inch gap, times board length). Joists are counted as width in inches divided by the spacing on center, plus one closing joist on the far edge. Screws multiply board rows by joists crossed, two per crossing. Footings use the cylinder volume πr²h per pier.
Every step is printed below the result with your own numbers substituted in, so you can check the math against your supplier's quote before you buy anything. Waste defaults to 10% — the standard allowance for straight cuts — and you can raise or lower it for diagonal layouts.
All results are planning estimates. Lumber prices, bag yields and code requirements vary by region; confirm quantities with your yard and the framing spans with your local building department.
Boards needed for common deck sizes
| Deck size | Area | 5.5" boards (12 ft) | With 10% waste | Joists at 16" o.c. |
|---|---|---|---|---|
| 8 × 10 ft | 80 sq ft | 15 | 16 | 7 |
| 10 × 12 ft | 120 sq ft | 22 | 24 | 10 |
| 12 × 12 ft | 144 sq ft | 26 | 29 | 10 |
| 12 × 16 ft | 192 sq ft | 35 | 38 | 13 |
| 16 × 20 ft | 320 sq ft | 58 | 64 | 17 |
Boards assume 5.5" face width, 12 ft length and a 1/8" gap (5.625 sq ft coverage each). Joists counted across the shorter dimension.
Frequently asked questions
How do you calculate the square footage of a deck?
Multiply length by width for a rectangle: a 12 × 16 ft deck is 192 sq ft. For L-shapes or odd layouts, split the deck into rectangles, calculate each one and add them together. Circles use π × radius². Our square footage calculator handles all three shapes.
What is the standard width of a deck board?
Standard 5/4×6 and 2×6 deck boards have an actual face width of 5.5 inches after milling, not the 6 inches the nominal name suggests. Wide 2×8 boards measure 7.25 inches. Always measure a board or check the mill sheet — coverage math depends on the real width.
How much waste should I add when ordering decking?
Add 10% for a simple rectangular deck with straight cuts, 15% for diagonal or herringbone layouts and multi-level designs where every board is cut to fit. Above 25% you are almost certainly over-ordering.
What gap should I leave between deck boards?
1/8 to 3/16 inch for wood decking — enough for drainage and seasonal movement without tripping the 1/4 inch code limit for walking surfaces. Composite boards typically install with 1/8 inch using the manufacturer's spacer clips.
How far apart should deck joists be?
16 inches on center is the residential standard for most deck boards. Use 12 inches for diagonal layouts or 5/4 boards, and 24 inches only with 2-inch-thick boards over short spans. Composite decking manufacturers usually cap spacing at 16 inches.
How many screws go in each deck board?
Two screws at every joist crossing. A 12 ft board over joists at 16 inches on center crosses about 9 joists, so it takes roughly 18 screws. Budget 10% extra for breakage and splits.
What is a board foot?
A board foot is a unit of lumber volume equal to 144 cubic inches — a board 1 inch thick, 12 inches wide and 12 inches long. Calculate it as (thickness × width × length) ÷ 12 using nominal dimensions. Hardwood yards price by board foot.
What is the difference between composite and wood decking?
Composite is a blend of wood fiber and plastic: it never needs staining, won't splinter and lasts 25–30 years, but costs roughly 2.5× pressure-treated wood per square foot and can fade. Wood is cheaper up front and looks natural, but needs sealing every 1–3 years.
How much does it cost to build a deck per square foot?
DIY materials run about $7–10 per sq ft for pressure-treated pine, $11–16 for cedar and $12–19 for composite, including framing and fasteners. Hiring a builder adds roughly $15–35 per sq ft in labor. Get local quotes — regional pricing varies widely.
What size lumber should I use for deck framing?
For a typical 12 ft span at 16 inches on center, a 2×10 Southern Pine #2 works (max span 16'4"). Shorter spans drop to 2×8 (13'7"). Species, grade and load all change the answer — check IRC 2021 Table R507.5 or your local equivalent.
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