Decking Board Calculator

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Decking Board Calculator

Calculation Summary

Total Deck Area:
Linear Meters Required:
Total Boards Needed:

*Results include the selected wastage allowance and board gaps.

How to Calculate Decking Boards

Planning a new outdoor space requires precision to ensure you order enough timber without excessive overspending. This decking board calculator helps you determine exactly how many lengths of timber you need based on your deck dimensions and the specific board profile you have chosen.

The Calculation Process

To calculate the number of boards, we use the following steps:

  1. Calculate Surface Area: Multiply the length by the width of the deck (e.g., 5m x 4m = 20m²).
  2. Effective Board Width: Add the board width (e.g., 140mm) to the gap width (e.g., 5mm). This gives 145mm (0.145m).
  3. Linear Meters: Divide the total area by the effective board width (20 / 0.145 = 137.93 linear meters).
  4. Wastage: Add 10% to account for offcuts and mistakes (137.93 * 1.10 = 151.72m).
  5. Board Count: Divide total linear meters by the length of a single board (151.72 / 5.4m = ~29 boards).

Important Considerations

When using this calculator, keep these professional tips in mind:

  • Board Gaps: Always leave a gap (usually 3mm to 6mm) between boards for drainage and expansion. Hardwood decks typically require larger gaps than composite decks.
  • Wastage: A standard 10% wastage is recommended. If your deck has a complex shape (hexagonal or diagonal boards), increase this to 15% or 20%.
  • Joist Spacing: While this tool calculates surface boards, remember that your subframe (joists) usually requires spacing of 400mm to 450mm centers for standard 19mm-25mm thick boards.

    • Example Calculation

    If you are building a deck that is 6 meters long and 3 meters wide using standard 90mm boards with a 5mm gap and 5.4m lengths:

    • Area: 18 m²
    • Effective Width: 95mm (0.095m)
    • Linear Meters: 189.47m
    • With 10% Waste: 208.42m
    • Total Boards: 39 boards (rounded up)
function calculateDecking() { // Get Input Values var deckL = parseFloat(document.getElementById("deckLength").value); var deckW = parseFloat(document.getElementById("deckWidth").value); var bWidth = parseFloat(document.getElementById("boardWidth").value); var bLength = parseFloat(document.getElementById("boardLength").value); var gap = parseFloat(document.getElementById("gapWidth").value); var waste = parseFloat(document.getElementById("wastage").value); // Validation if (isNaN(deckL) || isNaN(deckW) || isNaN(bWidth) || isNaN(bLength) || deckL <= 0 || deckW <= 0) { alert("Please enter valid positive numbers for all fields."); return; } // Calculations // 1. Total Area var totalArea = deckL * deckW; // 2. Effective Board Width (converted mm to m) var effectiveWidthM = (bWidth + gap) / 1000; // 3. Linear Meters needed (Area / Effective Width) var linearMeters = totalArea / effectiveWidthM; // 4. Apply Wastage var linearMetersWithWaste = linearMeters * (1 + (waste / 100)); // 5. Number of boards var boardsNeeded = Math.ceil(linearMetersWithWaste / bLength); // Display Results document.getElementById("resArea").innerText = totalArea.toFixed(2) + " m²"; document.getElementById("resLinear").innerText = linearMetersWithWaste.toFixed(2) + " m"; document.getElementById("resBoards").innerText = boardsNeeded + " Boards"; // Show Results Div document.getElementById("deckResults").style.display = "block"; }

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