🪵 Decking Material Calculator
Decking Boards Needed
0 linear m
Number of boards
0
Deck area
0 m²
Joists needed
0
Screws needed
0
How to Calculate Decking Materials
Estimating decking materials accurately saves you money and avoids project delays. Here's what this calculator covers:
- Decking boards — calculated as the number of boards across the width × the deck length, including the gap between each board
- Joists — spaced at standard 450 mm centres, running the shorter direction of your deck
- Screws — based on 2 screws per joist intersection, standard practice for 86–140 mm boards
This calculator assumes boards run along the length of the deck. For diagonal or herringbone patterns, add 15–20% extra to the board estimate.
Standard Decking Board Sizes
| Board Type | Common Width | Recommended Gap |
|---|---|---|
| Treated Pine | 86 mm, 120 mm | 3–5 mm |
| Hardwood (Merbau, Spotted Gum) | 86 mm, 120 mm, 140 mm | 4–5 mm |
| Composite Decking | 120 mm, 140 mm, 150 mm | 4–6 mm (per manufacturer) |
| Modular Tiles | 300 mm, 500 mm | N/A (interlocking) |
Worked Examples
Example 1 — Standard 5 m × 4 m Deck, 86 mm Boards, 4 mm Gap
| Item | Value |
|---|---|
| Deck dimensions | 5 m × 4 m |
| Board width + gap | 90 mm |
| Number of boards | 44 |
| Linear metres needed | 220 lm |
| Joists (450 mm centres) | 10 |
| Screws | ~880 |
Example 2 — Large Entertainer's Deck, 8 m × 6 m, 120 mm Boards
| Item | Value |
|---|---|
| Deck dimensions | 8 m × 6 m |
| Board width + gap | 124 mm |
| Number of boards | 48 |
| Linear metres needed | 384 lm |
| Joists (450 mm centres) | 14 |
| Screws | ~1,344 |
Frequently Asked Questions
How much extra should I order for wastage?▾
Allow 10% extra on decking boards and 5% on joists for offcuts, defects and mistakes. For curved or angled decks, increase wastage to 15–20%. This calculator automatically adds 10% to the board estimate.
Do I need to use 450 mm joist spacing?▾
450 mm centre-to-centre is standard for residential timber decking and is code-compliant under the National Construction Code. For composite decking, check manufacturer specs — many require 400 mm spacing. For commercial or high-traffic areas, consider 350 mm.
How many screws per decking board?▾
Two screws per joist intersection is standard. So for a 5 m deck with joists at 450 mm centres (10 joists), each board needs 20 screws. The calculator uses this formula. Use stainless steel or coated decking screws for corrosion resistance.
Do I need a bearer in addition to joists?▾
Yes — bearers run perpendicular to joists and sit on the posts/stumps. This calculator estimates joists only. For a complete estimate, budget for 2–3 bearers (typically 100×50 or 150×50 treated pine) spanning the length of the deck, plus posts at 1.5–1.8 m intervals.
Disclaimer: This calculator provides estimates based on standard Australian deck building practices. Always check local council requirements and the National Construction Code before ordering materials. Engage a licensed builder or structural engineer for complex deck designs.
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