Lumber calculator
Deck Board Calculator
Estimate straight board rows, stock boards to buy, and material cost from actual deck and board dimensions.
Planning estimate, not a contractor quote. Review the assumptions and replace presets with local prices when available.
Method
How this calculator works
Board width and edge gaps together determine how many rows cover a deck. This tool allocates full stock boards to each row before adding a purchase allowance. It deliberately avoids assuming every offcut can be reused, which would understate quantity for many layouts.
Rows = ceil((deck width inches + gap) ÷ (actual board width + gap)). Stock per row = ceil(deck length ÷ stock length). Purchased boards = ceil(rows × stock per row × allowance factor).
Worked example
A realistic starting point
A deck 12 ft across the boards with 5.5-inch boards and 0.25-inch gaps needs 26 rows. If each row is 16 ft long and stock boards are 16 ft, the base count is 26 boards. With 10% purchase allowance, buy 29 boards.
What changes the answer
Factors worth checking
Actual width and spacing
Use the measured board width and the specified edge gap. Nominal lumber sizes or one universal gap can produce the wrong row count.
Stock and offcuts
Each row receives its own stock allocation. If you have a supported cutting plan that reuses offcuts, compare it with this conservative quantity.
Beyond straight rows
Picture frames, diagonal layouts, stairs, end-gap details, and seam supports need a separate takeoff. The result does not size joists or establish permitted spans.
Common questions
Deck Board FAQ
Can I compare 12 ft and 16 ft stock?
Yes. Change stock length and price. The result reflects complete stock allocations per row, not only total linear footage.
Does board gap change quantity?
Yes. The row count accounts for gaps between adjacent boards, without adding an extra outside gap.
Does the allowance design a cutting plan?
No. It adds purchase stock; each actual end joint still needs the specified support and layout.
Evidence
Sources & review
- Trex — deck board spacingBoard spacing depends on the product and installation method.
Published by Calcstead. Report a correction.
Method and source links reviewed September 6, 2026. Price presets are editable planning inputs and should be replaced with current local information.