Decking Calculator
Boards, gaps, joists and screws for a rectangular deck.
Deck
= 192" (16')
= 144" (12')
Advanced
= 5 1/2"
= 192" (16')
= 3/16"
= 16" (1' 4")
Results update as you typeLive
Decking · Result
! Check failedBOARDS TO BUY
29 boards to buy
- Boards across
- 26
- Linear feet
- 416'
- Joists
- 13
- Screws
- 676
surplus exceeds the 1/2 in maximum overhang; rip the last board to 1 13/16"
Waste allowance 10%
SUGGESTED DEFAULTChangeNo edge gaps by default; an edge abutting a structure needs its own gap
SUGGESTED DEFAULTCode references & assumptions · 2
How this result is supported
- SUGGESTED DEFAULTNo edge gaps by default; an edge abutting a structure needs its own gap
- UNVERIFIED
- ASSUMPTIONStock boards come from gross linear length; offcuts are reusable across runs
- ASSUMPTION
What do these evidence labels mean?
- PRIMARY-VERIFIED
- directly supported by one authoritative primary source, quoted with section/page/figure
- CROSS-VERIFIED
- independently supported by two or more appropriate authoritative sources
- DERIVED
- mathematically derived from PRIMARY-VERIFIED values; the derivation is preserved in data and in code
- INTERPRETED
- a source exists but translating it into calculator behaviour required interpretation
- CONVENTION
- recognised trade practice, not a mandatory provision
- ASSUMPTION
- product/design assumption or useful default with no authoritative basis
- UNVERIFIED
- insufficient authoritative evidence
Code references and product data are quoted in the units their source uses.
Reference checks are informational, not compliance determinations.
How decking is calculated
Boards are counted across the deck's width, not over its area: what matters is how many board-plus-gap pitches fit the run the boards have to cover. The calculator reports the last board's rip width, because a deck that ends in a one-inch sliver is a layout to reconsider before it is a cut to make.
The gap is a real input rather than a rounding convenience. Wood shrinks and composite moves with temperature, and manufacturers publish different gaps for each, so the calculator asks rather than assuming a number and hiding it in the board count.
Boards are sold in stock lengths, so a deck longer than one board needs butt joints, and every butt joint needs a joist under it. The joist count includes those extras rather than leaving them to be discovered when the boards land short.
Five-quarter (5/4) decking is nominally 1.25 inches and dressed to about 1 inch actual. It changes nothing here — thickness plays no part in a board count — but it matters when the same stock is priced in board feet, which is calculated on the nominal size.
board pitch = board width + gap
boards = ceil((deck width + gap) ÷ pitch)
linear feet = boards × deck length