Decking Calculator
Estimate deck boards, courses, joists, screws, fastener packs and material cost for a rectangular deck.
Default project preview
29 boards
Deck area
192 ft²
Board courses
26
Joists
14
Fasteners
576
Calculator
Build the material order
Your order will appear here
Enter the project details and calculate a rounded material estimate.
Methodology
Transparent calculation
BuildMeter converts every input to a consistent internal unit, applies the selected allowance, and rounds products up to whole purchasable units.
Courses = deck width ÷ (board face width + gap). Boards = courses × boards per course × waste factor. Joists = round up (deck length ÷ spacing) + 1.
BuildMeter Guides
Understand the measurements and assumptions
Use these visible reference guides before changing project inputs or planning allowances.
FAQ
Decking Calculator questions
Which direction do the deck boards run?+
This calculator assumes boards run along the entered deck length and joists run perpendicular to them.
How much decking waste should I add?+
Ten percent is common for straightforward layouts. Diagonal boards, picture frames and complex cuts need more.
Does this calculate structural beams and footings?+
No. Structural members depend on spans, loads, species, soil and local building code.
Project guide
Use this calculator with confidence
Last reviewed: July 19, 2026
The decking calculator estimates deck boards, linear footage and material cost from deck dimensions, board width, spacing and waste. It models the walking surface only; framing, footings, railings, stairs, fasteners and local structural requirements are separate. Use actual board dimensions rather than nominal size, and decide board direction before measuring because span direction changes the required board lengths and cuts.
How to use it
- 1Measure the finished deck width and projection.
- 2Choose board direction and enter actual face width.
- 3Include the intended gap between boards.
- 4Adjust waste for butt joints, picture framing, angles and stock lengths.
Worked example
A 12 ft × 16 ft deck is 192 ft². With 5.5 in. boards and 0.25 in. gaps, each course occupies 5.75 in. The number of courses is rounded upward, then total linear footage receives the selected waste allowance.
What the defaults mean
Actual board width
Use measured face width, not the nominal lumber name.
Board gap
An editable layout input; product and moisture condition affect spacing.
10% waste
A straight rectangular starting point.
| Detail | Quantity effect | Plan separately |
|---|---|---|
| Straight field boards | base linear footage | stock lengths and butt joints |
| Picture-frame border | adds perimeter boards | miter cuts and blocking |
| Diagonal layout | increases cuts | larger waste allowance |
Common measurement mistakes
- Using nominal 6 in. width for a narrower finished board.
- Ignoring gaps in the course count.
- Measuring area without choosing board direction.
- Omitting picture-frame borders and breaker boards.
Limits and safety
- Not a joist, beam, ledger or footing design tool.
- Spacing and fastening must follow product and project requirements.
- Railing, stairs and trim are separate quantities.
Continue the project
plan deck-board spacing — Compare board width, gaps and course count.
estimate deck screws — Use joist spacing and fasteners per intersection.
estimate deck joist quantity — Plan framing independently of surface boards.
calculate deck railing materials — Measure open edges and post spacing.