Deck Board & Material Calculator
Estimate decking rows, board quantities and surface material cost for a rectangular deck. Compare boards running in either direction and include your own waste allowance.
How the board estimate works
Rows = (cross-deck width + gap) ÷ (actual board face width + gap), rounded up. The added gap in the numerator accounts for there being one fewer gap than rows. The final row may need trimming. Board run is the deck dimension in the selected direction.
The conservative estimate rounds each row up to whole stock boards and does not reuse offcuts between rows. A separate linear-length lower bound assumes perfect offcut reuse. Neither is an optimized cutting plan. Additional allowance is applied after these quantities are calculated.
Worked example
A 16 × 12 ft deck with 5.5-inch boards and 0.25-inch gaps needs 26 rows. With 16-ft stock running along the length, that is 26 boards before allowance, or 29 boards with 10% extra.
Which width and gap should I enter?
Use the actual finished face width, not a nominal lumber size. Obtain side gaps, end gaps and expansion clearances from your chosen product installation guide. This estimate models side gaps only; it does not subtract perimeter or butt-joint clearances.
Does this include the full deck structure?
No. This deck material calculator estimates the surface boards only. Joists, beams, footings, posts, railings, fasteners, fascia, stair parts, labour and tax are excluded. Structural spans and supports require separate design.
What about diagonal decking or picture-frame borders?
This calculation is for straight rows on a rectangle. Angled layouts, borders, breaker boards and cut-outs need a separate cutting plan. Butt joints require suitable support; confirm the layout before ordering.
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