Deck Board Calculator
How many decking boards to buy after gap and waste — quantity, not a deck bid. Click any i for detail.
Decking
Deck area (sq ft)
i
Area
Walking surface. Stairs and picture-frame borders need extra waste. |
|
|---|---|
Board width (in)
i
Board width
A 5/4×6 is often 5.5 in actual. Composite widths vary by brand. |
|
Board length (ft)
i
Board length
Stock length you are buying (12, 16, 20 ft). |
|
Gap (in)
i
Gap
Hidden-fastener or butt gap. ~1/8 in is common for wood; composites follow the clip. |
|
Waste (%)
i
Waste
Rips, stairs, and picture-frame. 10% is a common adder. |
How to use this calculator
- Enter deck square footage.
- Set actual board width and stock length.
- Include the gap your fasteners require.
- Add waste, then round up to whole boards.
Results explained
Cover width = board + gap. Linear feet = area ÷ cover width. Boards = linear feet ÷ stock length, then × (1 + waste%). Joists and footings are not counted.
Quick reference: decking
Buy extra from the same dye lot on composite.
| Item | Detail |
|---|---|
| 5/4×6 actual width | ~5.5 in |
| 12-ft board over 240 sq ft | See result after gap + waste |
| Picture-frame border | Raise waste |
| Labor? | See related deck / lumber cost pages |
Framing (joists, beams, posts) is a separate takeoff.
How the estimate is built
lf = area ÷ ((width + gap) / 12). boards = ceil( (lf / length) × (1 + waste%) ).
Example scenario
240 sq ft, 5.5 in board + 1/8 in gap, 12 ft stock, 10% waste → on the order of 50 boards.
FAQ
Joists too?
Not on this page — board count only.
Diagonal decking?
Raise waste; coverage math still starts from area ÷ cover width.
Install dollars?
Use deck-related cost calculators on the hub for labor midpoints.