Deck Board Calculator
Enter your deck dimensions and board size to estimate the number of deck boards, including a waste factor and optional cost.
Results
- Deck boards needed
- 29
- Deck area
- 192 sq ft
- Coverage per board
- 7.5 sq ft
Estimates only. Round up and buy a little extra to account for waste, spills, and breakage.
This calculator returns deck board counts by length, plus joists and fasteners, so you can hand a real cut list to the lumber yard.
Board coverage depends on the gap you leave. A 5.5 inch board with a 1/4 inch gap actually covers 5.75 inches of deck width.
Also works as a decking board calculator, deck screw calculator, and joist count estimator.
How to use the deck board calculator
- Enter the deck length in ft.
- Enter the deck width in ft.
- Enter the board width in in.
- Enter the board length in ft.
- Enter the gap between boards in in.
- Enter the waste factor in %.
- Optionally add a price to estimate the total project cost.
- Read your quantities instantly — no sign-up, and you can print the estimate to take to the supplier.
Worked example
Inputs
- Deck length
- 16 ft
- Deck width
- 12 ft
- Board width
- 5.5 in
- Board length
- 16 ft
- Gap between boards
- 0.125 in
- Waste factor
- 10 %
Results
- Deck boards needed
- 29
- Deck area
- 192 sq ft
- Coverage per board
- 7.5 sq ft
Using the example values above, the deck board calculator returns 29 (deck boards needed). Change any field to match your own project and the numbers update instantly.
Spacing, joists and screws
Joists are typically 16 inches on centre for perpendicular decking and 12 inches on centre for diagonal patterns or most composite brands.
Figure two screws per board at every joist crossing. A 12 by 16 ft deck with 16 inch joists needs roughly 500 to 600 deck screws.
Board length strategy
Buy boards that span the full deck width where possible. Butt joints must land on a joist and look best when staggered rather than lined up.
Add 10 percent for waste, or 15 percent for a picture frame border or diagonal layout where every board is cut at an angle.
How much extra should I order?
Always order a little extra. A 5% waste factor suits simple, square projects; 10% is right for most jobs; bump it to 15–20% for irregular shapes, diagonal patterns, or uneven ground. Running short almost always costs more than the leftover material.
Nominal vs actual (dry)
| Nominal | Actual |
|---|---|
| 1×4 | 3/4 × 3 1/2 in |
| 1×6 | 3/4 × 5 1/2 in |
| 2×4 | 1 1/2 × 3 1/2 in |
| 2×6 | 1 1/2 × 5 1/2 in |
| 2×8 | 1 1/2 × 7 1/4 in |
| 2×12 | 1 1/2 × 11 1/4 in |
Formula
Boards = deck area ÷ board coverage, × (1 + waste%). Board coverage = (board width + gap) × board length.
Frequently asked questions
- What gap should I leave between deck boards?
- Leave 1/8 in for kiln-dried boards; wet pressure-treated boards can be butted tight since they shrink.
- How much waste should I add?
- Add 10% for straight decks and 15% for diagonal or picture-frame patterns.
- How many deck boards do I need?
- Divide deck width in inches by board width plus gap, then multiply by the number of rows required for the deck length.
- What gap should I leave between deck boards?
- 1/8 inch for wet pressure treated lumber, which shrinks as it dries, and 1/4 inch for dry or composite boards.
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