Decking: boards, joists, screws and the full list
A deck's materials come from its size, the board width and the joist centres. A 4 x 3 m deck in 144 mm boards needs 26 boards of 3.6 m, 11 joists at 400 mm centres and 462 screws, with 10% extra boards for cuts.
This page gathers our UK decking calculators and guides: boards, joists, screws, weed membrane, oil and steps. The garden planner puts them in order with fencing and the shed.
Decking materials by size
144 mm boards in 3.6 m lengths with 5 mm gaps, joists at 400 mm centres and 10% extra boards, worked out by the decking calculator.
| Deck (metres) | Area (m²) | Boards | Joists | Screws |
|---|---|---|---|---|
| 2.4 x 2.4 | 5.8 | 19 | 7 | 238 |
| 3 x 3 | 9.0 | 24 | 9 | 378 |
| 4 x 3 | 12.0 | 26 | 11 | 462 |
| 4 x 4 | 16.0 | 33 | 11 | 594 |
| 5 x 4 | 20.0 | 42 | 14 | 756 |
| 6 x 4 | 24.0 | 50 | 16 | 864 |
Boards, screws and the full list
Boards are counted in rows across the deck and lengths along each row. Choose a board length that suits the deck so joins land on joists. The materials calculator adds weed membrane and decking oil to the list.
Joists
Joists at 400 mm centres suit most softwood and composite boards; check the board maker's maximum span. The joist calculator counts joists, strutting and the timber to buy for your span.
Steps
A raised deck needs steps with an even rise and going. The stair calculator works out the number of steps from the total height.
Every calculator for this topic
Guides
- Common Mistakes Building Decking (UK): Boards, Joists, GapsDecking mistakes: joist spacing, board gaps, ground prep. A 4 × 3 m deck with 144 mm boards needs 31 boards of 3 m and 11 joists at 400 mm.
- Decking or Paving for a Garden? What Each Needs, 4 x 3 mCompare decking and a paved patio for a 4 x 3 m garden area: what to buy, the groundwork, upkeep, and which suits a sloping or damp garden.
- How Many Floor Joists Do I Need? Spacing and Strutting (UK)A floor 5 m long needs 14 joists at 400 mm centres. Charts of joists at 400, 450 and 600 mm, the cut length, and when you need strutting.
- Staircase Regulations UK: Rise, Going, Pitch and Number of StepsA 2,600 mm floor to floor height needs 14 risers of 186 mm. Part K limits a private stair to a 220 mm rise, 220 mm going and a 42° pitch.
- Decking Materials List UK: Boards, Joists and ScrewsThe boards, joists and screws for a 4 × 3 m garden deck, with a size chart, the planning rules and how the numbers were worked out.
Other guides that use these calculators: How Many Loft Boards Do I Need? Area, Thickness and Screws (UK) · Garden Fence Materials List UK: Panels, Posts, Gravel Boards
Answers for common sizes
Already know the size? These pages give the worked answer for one common size each, with the inputs filled in so you can adjust them.
Project planners
Planning the whole job rather than one material? These step-by-step planners put the calculators above in the order you will need them.
Frequently asked questions
How many decking boards for a 4 x 3 m deck?
26 boards of 144 mm in 3.6 m lengths, including 10% for cuts.
What joist spacing for decking?
400 mm centres for most softwood boards and many composites; some composite makers ask for 300 or 350 mm, so check the fitting guide.
Do I need planning permission for decking?
In England, decking is permitted development if it is no more than 30 cm above the ground and, with other extensions and outbuildings, covers no more than half the garden. Higher platforms need permission.
How many screws for decking?
Two at every joist crossing: 462 for a 4 x 3 m deck in 144 mm boards.
Related topics
Estimates only. Quantities depend on your materials, site and supplier, so check pack sizes and coverage on the label. Check the Building Regulations and any planning rules for anything structural or close to a boundary. How we calculate.