Deck Material Calculator
Estimate decking boards and material cost for your deck
Decking (surface boards) only — framing and footings depend on local building code span tables.
Frequently Asked Questions
Divide your deck's total area by the effective width of one board (the board's face width plus the gap left between boards), which gives the total linear footage of decking needed. Then divide that by the length of board you're buying to get a board count, and add a waste factor for cuts.
1/8 inch (0.125") is the standard gap for pressure-treated lumber to allow for drainage and future expansion. Composite decking often uses a similar or manufacturer-specified gap — check your product's installation guide.
No — this calculator estimates decking (the visible surface boards) and fastener count only. Framing (joist sizing, beams, footing depth) depends on span tables governed by your local building code and the specific lumber species/grade, which this tool doesn't calculate — consult your local code or a contractor for structural framing.
A common rule of thumb is 2 screws per board at each joist crossing — roughly 350 screws per 100 sq ft of decking at 16" joist spacing, or about 467 screws per 100 sq ft at 12" spacing (used for some composite decking). This calculator estimates fastener count from your deck area and joist spacing.
10% is a reasonable default for a simple rectangular deck. Diagonal decking patterns, picture-frame borders, or decks with lots of cuts around posts typically need 15-20%.
How deck boards are calculated
- Effective board width = board face width + gap, converted to feet.
- Linear feet = deck area ÷ effective width, plus the waste allowance.
- Boards = linear feet ÷ board length, rounded up.
- Screws: two per board at every joist, about 350 per 100 sq ft at 16-inch joist spacing or 467 at 12 inches.
Example
A 16 × 12 ft deck is 192 sq ft. With 5.5-inch boards and a 1/8-inch gap, each board covers 0.469 ft of width, so you need about 410 linear feet, or 451 ft with 10% waste. That is 38 boards 12 ft long and about 672 screws at 16-inch spacing.
Board sizes
| Board | Actual width | Notes |
|---|---|---|
| 5/4 × 6 (wood) | 5.5 in | most common decking |
| 2 × 6 (wood) | 5.5 in | thicker, spans 24-inch joists |
| Composite | about 5.5 in | often needs 12 or 16 in joist spacing; check the brand |
Gaps
- Wet pressure-treated wood: install tight or with a very small gap; boards shrink as they dry.
- Kiln-dried wood: about 1/8 inch between boards.
- Composite and PVC: follow the manufacturer, often 3/16 to 1/4 inch side to side, plus end gaps that depend on temperature.
Ordering tips
- Choose a board length that spans the deck or splits evenly at a joist to reduce waste and avoid butt joints.
- Use 10% waste for simple decks and 15% to 20% for diagonal layouts or picture-frame borders.
- Hidden clip fasteners replace face screws on many composite boards; count clips per the manufacturer.
This calculator covers the decking surface only. Joists, beams, posts and footings depend on span tables in your local building code, and most decks attached to a house need a permit.
Estimate framing with the lumber calculator, add a railing with the linear foot calculator, and plan an accessible entrance with the ramp calculator.