Calculator
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How deck materials are estimated
A deck's material list comes down to four things: the deck's total area, the width of the boards you're using, the gap between them, and the joist spacing. This calculator handles the math, and also returns total linear feet and a cost estimate so you can budget before you head to the lumber yard.
Common decking board sizes
| Board type | Nominal | Actual face width |
|---|---|---|
| 5/4 decking | 5/4 × 6 | 5.5 in |
| Pressure-treated 2×4 | 2 × 4 | 3.5 in |
| Pressure-treated 2×6 | 2 × 6 | 5.5 in |
| Pressure-treated 2×8 | 2 × 8 | 7.25 in |
| Composite (metric) | 140 mm | 5.5 in |
Joist spacing rules of thumb
- 12" O.C. — required for most composite decking and diagonal layouts
- 16" O.C. — standard for wood decking running perpendicular to joists
- 24" O.C. — only allowed for certain engineered wood boards; check manufacturer specs
Always check your local building code and the decking manufacturer's installation instructions before building. Joist spacing has structural implications, not just material counts.
How to use this calculator
- Enter your deck's length and width in feet.
- Choose the decking board type you plan to use.
- Select your board length (usually 8, 12, or 16 ft).
- Adjust gap and joist spacing if you have specific plans.
- Enter current prices to estimate total cost.
- Click "Calculate materials" to see your shopping list.
Frequently asked questions
How many deck boards do I need for a 12×16 deck?
For a 12×16 ft deck (192 sq ft) using standard 5/4×6 boards at 16" joist spacing with a 1/8" gap, you need approximately 41 boards if using 16 ft lengths, or 82 boards if using 8 ft lengths. This calculator gives the exact number for your specific dimensions.
Should I run deck boards parallel or perpendicular to the house?
Perpendicular (boards running away from the house) is the most common and structurally straightforward. Parallel layouts can work but require blocking between joists. Diagonal layouts look distinctive but need 12" joist spacing and generate more waste.
What is the ideal gap between deck boards?
1/8 inch (3 mm) is standard for most wood and composite decking. Pressure-treated wood shrinks slightly as it dries, so 1/8" is safe. Composite decking usually has specific gap requirements — check the manufacturer's spec.
How many screws do I need per board?
Two screws per joist per board. For a 12×16 deck with 16" joist spacing, that's roughly 2 screws × 13 joists × 41 boards = about 1,066 screws. This calculator estimates based on your specific dimensions and adds a 10% buffer.
Should I add a waste factor?
Yes. Always order 10% extra material for cutting waste, defects, and future repairs. For diagonal layouts, increase to 15%. This calculator reports the minimum needed; buy 10% more than the estimate.