Calculate deck boards needed for your outdoor deck project with direction-specific waste factors.
Part of the Surfaces & Finishes calculators — see all tools in this category.
Length of deck (parallel to house)
Width of deck (away from house)
5.5" is most common for residential decks
Match to deck dimension to minimize splices
Standard: 1/8" (0.125)
Add for complex shapes or extra material
12 ft boards
Total board length
12' × 12'
Measure your deck frame or planned deck size. Length is typically parallel to your house, width extends away from the house. For irregular shapes, calculate the bounding rectangle.
Standard deck boards are 5.5" (nominal 6") wide. Narrow 3.5" boards create a different look, while 7.25" wide boards cover faster but can cup more in sun exposure.
Match board length to minimize splices. 8, 10, 12, 16, and 20-foot lengths are standard. Longer boards mean fewer joints but are heavier and harder to handle.
Lengthwise: Boards run parallel to deck length - most common, 10% waste.
Widthwise: Boards run parallel to deck width - same waste factor.
Diagonal: 45-degree pattern - striking look but 20% waste for angled cuts.
The calculator accounts for gap spacing when determining how many boards fit across your deck. Standard 1/8" gap allows for drainage and prevents trapping debris.
The calculator shows boards needed (rounded up) and total linear feet for ordering. Order the exact quantity shown - waste factor is already included.
| Direction | Waste | Best For |
|---|---|---|
| Lengthwise | 10% | Most decks - boards parallel to house |
| Widthwise | 10% | Narrow decks, wrap-around porches |
| Diagonal (45°) | 20% | Visual interest, hiding imperfections |
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