Decking Boards Calculator
Fast, accurate and free online desek tarasowych calculator tool running directly in your browser.
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Deck board calculator
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Other tools you may find usefulHow does the decking board calculator work and why is it worth using?
The terrace board calculator is a practical online construction tool dedicated to people planning to build a wooden or composite terrace. Building a terrace is a great way to expand the living space of your home, but the costs of boards (especially those made of exotic wood or high-quality composite) are high. Correct calculation of the number of linear meters (m) and pieces of boards of a specific length prevents material shortages during installation and optimizes the investment budget.
The calculator calculates the demand for boards based on the terrace area (m²), board width (mm), planned distance (expansion gap) between boards (mm) and the length of a single board (m).
How to calculate the demand for terrace boards?
The calculation is based on the effective covering width of a single row of boards:
Effective width (m) = [ Board width (mm) + Gap (mm) ] / 1000
The total length of the boards in running meters (mb) is determined by the formula:
Running meters (mb) = Terrace area (m²) / Effective width (m)
Multiply the result by the stock (usually **10%** for transverse cuts) and divide by the commercial length of the board (e.g. 3m or 4m) to obtain the number of pieces.
Recommended expansion gap between terrace boards
The gap between terrace boards is crucial for the durability of the structure. Wood swells when exposed to moisture and shrinks during dry periods. Lack of appropriate expansion joints leads to boards buckling, screws being pulled out and joists rotting. The recommended gaps are:
- For softwood and larch boards: **5 mm to 7 mm**.
- For composite boards (WPC): **4 mm to 6 mm** (due to longitudinal thermal expansion).
Demand for 145 mm wide boards (Table for 20 m² of terrace)
| Gap width (mm) | Effective covering width (mm) | Running meters per 20 m² (without spare) | Number of 4m boards (with 10% spare) |
|---|---|---|---|
| 3 mm expansion joints | 148 mm | 135 m | 38 pcs. |
| 5 mm expansion joints | 150 mm | 133 m | 37 pcs. |
| 7 mm expansion joints | 152 mm | 131 m | 36 pcs. |
Frequently asked questions (FAQ)
How many 4 m long boards are needed for a 25 m² terrace?
Assuming a 145 mm board with a 5 mm gap (effectively 150 mm), the requirement is: 25 / 0.15 = 166.7 meters of boards. Adding 10% of the stock (183.3 m) and dividing by the length of 4 m, we get the result: you need to purchase 46 terrace boards.
Why is the stock for cutting terrace boards as high as 10%?
Terrace boards are most often laid staggered (wild or brick). Because structural joists have a fixed spacing (e.g. every 40-50 cm), each board cut must be exactly on the joist axis. This creates waste (cuts), hence a higher margin of stock is recommended.
What is the appropriate spacing of joists for terrace boards?
The standard spacing of joists for 24-28 mm thick boards is from 40 cm to 50 cm. For thinner composite boards or softwood, the spacing should not exceed 35-40 cm to avoid sagging of the floor.
What is the difference between a wooden terrace and a composite (WPC) terrace?
A wooden terrace (Siberian larch, exotic wood) has a natural appearance, but requires regular oil impregnation once or twice a year. Composite terrace (wood flour + PVC/PE) is almost maintenance-free and does not require painting, but it heats up significantly in the sun.
How to lay terrace boards: with the grooves up or down?
Traditionally, the boards were laid with the grooves facing upwards to drain water and prevent slipping. However, modern trends and manufacturers' recommendations allow the boards to be laid with the smooth side up, which makes cleaning, sweeping and renovating the terrace easier.