Decking Calculator
This professional decking calculator estimates rows, total boards, linear footage, and fasteners for rectangular decks. It supports imperial and metric units, common board profiles, joist spacing, board gaps, and waste allowance—ideal for homeowners, contractors, and estimators seeking fast, defensible takeoffs.
Decking Calculator Inputs
Pick a preset or keep “Custom” and specify the actual board width.
Results
Note: Results are estimates for rectangular fields. Add extra for borders, stair treads, and off-rectangle areas.
Data Source and Methodology
Authoritative reference: American Wood Council (AWC), “DCA 6 — Prescriptive Residential Wood Deck Construction Guide,” 2015 Edition (revised 2019). Access: awc.org/publications/dca6.
This estimator uses geometric coverage formulas to count rows and board pieces, and applies AWC DCA 6–aligned assumptions for joist spacing when estimating fasteners. Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.
The Formula Explained
$$R=\left\lceil \frac{C}{w+g} \right\rceil$$ $$B_r=\left\lceil \frac{L}{\ell_b} \right\rceil$$ $$B_{\text{raw}}=R \times B_r \quad\quad B_{\text{total}}=\left\lceil B_{\text{raw}} \times \left(1+\frac{p_w}{100}\right) \right\rceil$$ $$J = \left\lfloor \frac{\ell_b}{s_j} \right\rfloor + 1 \quad\quad F = 2 \times B_{\text{total}} \times J$$ $$A = L \times C$$
Where R = rows, C = cross dimension, w = board width, g = gap, L = run dimension, ℓ_b = board length, p_w = waste percent, s_j = joist spacing, J = joists crossed per board, F = fasteners, A = deck area.
Glossary of Variables
- L (Run dimension): The deck dimension parallel to the board orientation you select.
- C (Cross dimension): The deck dimension perpendicular to the board orientation.
- w (Board width): Actual face width of the deck board.
- g (Gap): Target spacing between adjacent boards.
- ℓ_b (Board length): Stock length of each board piece used.
- p_w (Waste %): Extra allowance for cuts, defects, and staggering.
- s_j (Joist spacing): On-center distance between joists.
- R (Rows): Number of side-by-side board rows across the deck.
- B_r (Boards per row): Number of board pieces required along the run direction to span the deck.
- B_total: Total boards to purchase after adding waste.
- F (Fasteners): Estimated screws assuming two per joist per board.
- A (Area): Deck surface area.
How It Works: A Step-by-Step Example
Example: 20 ft (L) by 12 ft (C) deck, boards 5.5 in wide (w), 16 ft long (ℓ_b), 0.125 in gap (g), orientation along length, joist spacing 16 in (s_j), waste 10% (p_w).
- Rows: R = ceil(144 / (5.5 + 0.125)) = ceil(25.85) = 26 rows.
- Boards per row: B_r = ceil(240 / 192) = 2 boards.
- Raw boards: B_raw = 26 × 2 = 52.
- Total boards incl. waste: B_total = ceil(52 × 1.10) = 58 boards.
- Joists crossed per board: J = floor(192 / 16) + 1 = 13.
- Fasteners: F = 2 × 58 × 13 = 1,508 screws (approx.).
- Area: A = 20 × 12 = 240 ft².
Frequently Asked Questions (FAQ)
Does this tool account for diagonal decking?
Not directly. For 45° layouts, increase waste (often 15–20%) and verify joist spacing per manufacturer recommendations.
What if my deck is not a perfect rectangle?
Estimate each rectangular section separately and sum results. Add additional waste for complex shapes and borders.
Can I mix board lengths to reduce waste?
Yes. Using a mix (e.g., 12 ft and 16 ft) may reduce offcuts. This calculator assumes a single length for simplicity.
How do hidden fasteners affect counts?
Hidden systems typically require one clip per joist per board plus starters/finishers. Check your system’s datasheet to convert from the screw estimate.
What board gap should I use?
Typical gaps range 1/8–1/4 in (3–6 mm). Follow manufacturer guidance considering moisture content, climate, and material type.
Is the joist count considered?
Fastener counts approximate joists crossed per board. This tool doesn’t calculate framing material; consult AWC DCA 6 and local code for spans and sizes.