How to use this calculator
- Enter finished deck length and width.
- Choose your board width, length, and intended gap.
- Set waste and the actual quoted price per board plus framing/labor allowances.
The calculation formula
Rows = ceil((deck width + gap)/(board width + gap)). Boards per row = ceil(deck length ÷ board length). Purchase boards = ceil(rows × boards per row × (1 + waste%)).
Worked example
A 12 × 10 ft deck with 5.5 in-wide boards, 0.25 in gaps, and 12 ft boards needs about 21 rows, or 21 boards before waste.
Assumptions and limitations
- Board seam optimization, stairs, edging, railings, and complex layouts are excluded.
- Framing allowance is not a structural plan; consult qualified designers for loads and code compliance.
Actual project costs may be affected by supplier rates, material grade, labor market, location, disposal, site condition, access, permits, taxes, and schedule. All entered prices are yours to revise. See our methodology and disclaimer.
Frequently asked questions
Does this design the deck frame?
No. The framing input is a budget allowance only; the tool makes no structural claims.
Why are board counts rounded?
You cannot generally buy fractions of a full-length board.