To estimate deck boards, you go from area to linear meters to board count: measure the square meters (or square feet), multiply by the linear meters per m² for your board width (about 8.3 with 120 mm / 4.7 in boards), and add roughly 10 % for cutting waste. The deck board calculator on this page does the whole calculation for you — here is how it works under the hood.
How the calculation works
1. Measure the area
Measure the length and width of the deck and multiply:
- Length: 6 meters (about 20 ft)
- Width: 4 meters (about 13 ft)
- Area = 6 × 4 = 24 m² (about 260 sq ft)
If the deck has multiple sections or angles, split it into rectangles and add them up.
2. From square meters to linear meters
How many linear meters of decking you need per square meter depends on the board width:
| Board width | Linear meters per m² |
|---|---|
| 95 mm | approx. 10.5 lm |
| 120 mm | approx. 8.3 lm |
| 145 mm | approx. 6.9 lm |
The rule of thumb is 1000 divided by the board width in millimeters — for a 120 mm (4.7 in) board that gives 1000/120 ≈ 8.33 linear meters per m². The full math, with tables for common deck sizes, is in deck board linear feet: how to estimate quantity. Narrower boards mean more screw rows and more work; wider boards mean fewer linear meters — read more about that trade-off in choosing deck board width.
For our example with 120 mm boards: 24 m² × 8.33 ≈ 200 linear meters (about 656 linear feet).
3. Add cutting waste
End cuts, trimming around obstacles, and the occasional reject board are normal. Add about 10 % for a simple rectangular deck, and 15 % for diagonal installation or a complex shape: 200 lm × 1.10 = 220 linear meters. Why that buffer matters, and when to increase it, is covered in deck board waste allowance.
4. From linear meters to board count
Divide by the board length you can buy: 220 lm / 4.2 m (about 14 ft) ≈ 53 boards. Round up, and where possible pick board lengths that match your deck dimensions — that reduces both butt joints and offcuts.
Choose your material
Your choice of decking affects appearance, durability, and long-term maintenance:
- Pressure-treated softwood — the most affordable and most common option, needs regular oiling or staining.
- Oil-treated / factory-finished pressure-treated wood — pre-finished surface straight from the supplier, less maintenance in the first years.
- Thermally modified wood and premium hardwoods — dimensionally stable boards with long service life and little upkeep, at a higher price.
- Composite decking — close to maintenance-free and color-stable, but the most expensive and with its own joist spacing requirements.
A more thorough comparison is in how to choose the right deck material.
Don’t forget the screws
Once the boards are estimated, the fasteners remain: plan for 35–40 screws per m² (about 3–4 per sq ft), based on two screws per board per joist. The calculator estimates this at the same time — see also estimate deck screws for your project.
Frequently asked questions
How many deck boards do I need per square meter?
With 120 mm (4.7 in) wide boards you need about 8.3 linear meters per m². A 4.2 m (14 ft) board therefore covers about 0.5 m² — so figure roughly 2 boards of that length per square meter.
How much extra should I buy?
Add about 10 % for cutting waste on a normal rectangular deck, and 15 % for diagonal installation or a layout with many angles and cutouts.
Should I account for the gap between boards?
Yes, and the calculator does it automatically. The 3–5 mm (about 1/8–3/16 in) gap means each board row covers slightly more than the board width, but the 1000/board-width rule of thumb already includes a small margin that in practice absorbs this.
Which board length should I choose?
Pick lengths that divide evenly into your deck dimensions to avoid unnecessary joints and offcuts. A 4.8 m (16 ft) deck run is a perfect match for 4.8 m boards, while 3.6 m (12 ft) boards would force a joint in every row.