Deck board calculator
When joists are already figured (or someone else is framing), you still need a clean board count. This page strips the problem down to coverage width, board face, gap, length rows, and waste. Same voice as the deck calculator, fewer framing fields — so you are not hunting joist toggles while standing in the composite aisle.
+10% so you don't come up short
Estimate only — not a contractor bid. Confirm bag yields and local codes before you pour or order.
When to use
Re-decking over existing joists; buying composite where board width is weird; double-checking a store cutting list.
When not to
Full structural redesign — use the deck calculator. Radius decks and herringbone — layout first.
Assumptions
Face width and gap in inches. Waste default 10%. Board length options (12/16/20 ft) affect pieces per row, not coverage width math.
Worked examples
Example 1
12 ft wide deck, 5.5 in face, 0.125 in gap, 16 ft long, 16 ft boards, waste 10%
→ across ≈ 26 boards; one board length covers; order ≈ 29 after waste
Example 2
same width, 20 ft deck with 12 ft stock
→ butt seams add pieces per row — count rows of joints, not only area
How it calculates
Count boards across the cover width, multiply by pieces per row from stock length, add waste.
- Enter cover width and deck length.
- Set board face, gap, and stock length you buy.
- Dial waste; read the board count.
boards across = ceil(cover_width_in ÷ (face_width_in + gap_in)) rows along length = ceil(deck_length ÷ stock_length) order = boards × rows × (1 + waste%), round up
Common traps
- Butt joints on short stock inflate piece count.
- Grooved vs square edge changes fasteners, not face coverage much.
- Color batch — buy extras from the same run.
- Rip the last board — still buy a full board.
Next tool
Need joists too → deck calculator.
Stairs → stair calculator.
FAQ
Cover width ÷ (face + gap), times length rows, plus waste.
Related
Estimate only — not a contractor bid or engineered takeoff. Confirm bag yields and local codes before you pour or order.