Project plan · Outdoor
3 × 4 m Ground-Level Deck: Decking Boards, Gaps and Screws
Decking for a 4 × 3 m surface with boards running the long way: 21 rows of 140 mm boards at 5 mm gaps, worked through for both metric and imperial stock. The plan covers the surface only and assumes a separately designed frame.
Calculated plan · Last updated
- Difficulty
- Intermediate
- Time
- 4 days
- Surface
- 4 × 3 m
- Rows
- 21 × 140 mm
- Est. cost
- ≈ $534
Cut list
| Part | Qty | Size L × W × T (mm) | Material / source |
|---|---|---|---|
| Deck board rowTrim about 200 mm from each board | 20 | 4000 × 140 × 22 | 140 × 22 mm decking4.2 m board |
| Final row, rippedRipped by 40 mm, or left to overhang | 1 | 4000 × 100 × 22 | 140 × 22 mm decking4.2 m board |
Kerf allowance: 3 mm per cut.
Layout
How the numbers were checked
- Deck Board Calculator, metric
- 21 rows, 20 boards of 4.2 m before waste, 22 with 10% waste (84 linear m).
- Deck Board Calculator, imperial stock
- 5½ in boards at ³⁄₁₆ in gaps: 21 rows, 22 boards of 14 ft with 10% waste.
- Row-by-row check
- One full-length board per row needs 21 boards, so the 22 bought leave 1 spare for defects.
- Coverage
- 21 rows cover 3,040 mm, 40 mm more than the 3000 mm width.
Build steps
Confirm the frame
Check that the frame is square, level and ready for decking, with joists at no more than 450 mm centres or the spacing the board manufacturer specifies. This plan assumes 10 joists at about 444 mm centres across the 4 m run.
Plan the last row first
21 rows cover 3,040 mm. Decide now whether the final row is ripped to 100 mm or overhangs the edge by 40 mm, so the first row can be set from the correct edge.
Lay the first row straight
Snap a line along the starting edge and fix the first board to it. Every following row takes its line from this one.
Fix each row with spacers
Set 5 mm spacers between rows and drive two screws into every joist, keeping screws a consistent distance from the board edges and pre-drilling near board ends.
Trim the ends
Let the boards run long, then snap a line and trim all the ends in one pass for a straight edge.
Assumptions
- Unit prices are assumed 2026 retail figures in US dollars for illustration only, not supplier quotes. Replace them with local prices before budgeting.
- This deck estimate covers surface deck-board quantities only. Deck framing materials, including joists, beams, posts, footings and perimeter framing, are not included.
- Joist count assumes 450 mm maximum centres and is used only to estimate screws.
- Boards are 140 mm wide as supplied. Measure your decking, because actual widths vary by product.
Safety and scope
- This is not engineering advice. Joist size, span, footings and fixings must be designed to local building rules and the decking manufacturer's instructions.
- Check whether your deck needs a permit or must meet height, balustrade or setback rules under local regulations.
- Wear eye protection and a dust mask when cutting treated or composite decking.
- Planning estimates only — verify before you buy or build. Read the disclaimer.
Quantity basis for each material
- Deck board, 140 × 22 mm × 4.2 m
- Deck Board Calculator result including 10% waste.
- Stainless deck screws, box of 250
- 420 screws: 21 rows × 10 joists × 2, plus 5% spare = 441.
- Gap spacers, 5 mm
- Keeps the 5 mm gap consistent between rows.