Decking board calculator
How many deck boards, rows and clips or screws your deck needs.
Your deck and the result
Your deck
Boards for a 4.80 m × 3.60 m deck
- Deck boards to buy
- 26boards 26 × 5.4 m lengths · Composite 137 × 23 (any brand)
- Deck area
- 17.3m²
- Board rows, running along the house
- 26
- Joist centres
- 396mm The board allows up to 400 mm
- Hidden deck clips
- 4boxes To suit Composite 137 × 23, box of 100
- Board offcut
- 11% 140.4 m bought, 124.8 m used
How the boards are laid: every board runs the full length in one piece.
Concept plan, not for construction
The full list
Decking boards and fixings
| Item | Specification | Qty | Unit |
|---|---|---|---|
| Composite 137 × 23 — Charcoal140.4 lm. Whole deck: 17.28 m², 26 rows, 140.4 lm of boards in total (11.1% offcut); 1 piece ripped to width. | 5.4 m lengths | 26 | pcs |
| Hidden deck clips338 clips: 1 per board at each of 338 board-over-joist crossings. Check whether clip screws are included. | To suit Composite 137 × 23, box of 100 | 4 | boxes |
| Starter / edge-board screwsTo face-fix the first and last boards (or use the clip maker’s starter clips). | Colour-matched composite deck screws, ≈ 10g × 60 mm | 1 | boxes |
| Framing anchors (joist to bearer)One at each of 52 places where a joist crosses a bearer. | Galvanised, with galvanised nails / screws | 52 | pcs |
| Post caps / bearer saddles (post to bearer)One per post. Each bearer sits on top of its post and is held down with a galvanised post cap or saddle (or a stirrup and strap), nailed or screwed as its manufacturer specifies. | Galvanised, to suit 90 × 90 posts under 190 × 90 bearers, fixed per manufacturer | 12 | pcs |
| Galvanised framing nails / screwsFor rims, blocking and laminating double bearers. | 1 kg box, hot-dip galvanised | 1 | boxes |
The framing underneath, from the same run of the engine
| Item | Figure |
|---|---|
| Joists | 90 × 45 MGP10 H4 at 396 mm centres (Treated pine MGP10 (H3 / H4)) |
| Longest joist span | 1,170 mm |
| Bearers | 2 / 190 × 45 MGP10 H4 (double), 4 lines |
| Posts | 12 × 90 × 90 H4 post |
| Footings | 12 pads, 300–400 mm square |
| Clearance under the lowest member | 147 mm |
How this is worked out
Each row of Composite 137 × 23 (any brand) covers its width plus the gap beside it: 137 + 6 = 143 mm. The engine lays rows across the deck. Composite boards come in one length, so a deck longer than one board gets breaker boards (boards laid across the others) and the rest run in one piece. It cuts each row from the stock lengths that leave the least offcut, and counts a clip (or a pair of screws) at every place a board crosses a joist.
The figures come from the same engine as the free deck designer, run on the server for a rectangular deck against the house. The span tables behind its framing have been checked by a structural engineer, but every framed figure is still a concept figure: concept plan, not for construction. Have a builder, building surveyor or certifier check any design before you build it.
Cutting and waste
Cut plan
| Material | Stock bought (m) | Cut (m) | Waste |
|---|---|---|---|
| Composite 137 × 23 — Charcoal | 140.4 | 124.8 | 11% |
| 90 × 45 MGP10 H4 — joists | 46.8 | 45.6 | 3% |
| 90 × 45 MGP10 H4 — rim joists | 9.6 | 9.6 | 0% |
| 2 / 190 × 45 MGP10 H4 (double) — bearers | 19.2 | 19.2 | 0% |
| 90 × 90 H4 post — posts | 2.4 | 1.8 | 27% |
The engine’s checks (3)
Checks
| Check | Detail |
|---|---|
| Extra rot protection near the ground | 19 frame pieces sit 400 mm or less above the ground. Wood this close to the ground gets extra rot protection (H4 treatment) instead of H3. Posts are always H4. Nothing for you to do. |
| Last row of boards ripped to 25 mm | The last row of boards has to be ripped (cut down lengthwise) to 25 mm wide — a full board is 137 mm. To finish on a full board, make the deck depth (out from the house) 31 mm smaller (3569 mm) or 112 mm larger (3712 mm). Strips narrower than about 69 mm are hard to fix down and can split or cup. |
| Council approval — VIC | In Victoria every deck attached to the house needs a building permit from a building surveyor, whatever its size. A planning permit from the council is usually not needed when the floor is 800 mm or less above the ground, unless a heritage or other overlay applies. Your deck is 17.3 m² and 450 mm high — confirm the requirements with your council before you build. |