Building a deck is a rewarding project, but accurate material estimation is crucial for both budget and efficiency. This calculator helps you determine the number of decking boards you'll need, taking into account the dimensions of your deck, the size of the boards, the spacing between them, and a factor for wastage.
How the Calculation Works
The core of this calculation involves determining the total linear meters of decking required for your deck surface and then dividing that by the usable length of a single board. We also account for the space between boards and potential material loss during cutting and installation.
Step 1: Calculate Deck Area
First, we find the total surface area of the deck you intend to build.
Deck Area (m²) = Deck Length (m) * Deck Width (m)
Step 2: Calculate Usable Board Width
Decking boards are typically laid side-by-side with a small gap for expansion and drainage. The effective width a board covers, including its gap, is its actual width plus the gap width. Remember to convert all units to meters for consistency in this step.
Step 3: Calculate Total Linear Meters of Decking Needed
To find out how many linear meters of decking material are needed to cover the entire deck area, we divide the deck's area by the usable width of a single board.
Total Linear Meters = Deck Area (m²) / Usable Board Width (m)
Step 4: Calculate the Number of Boards (Before Wastage)
Now, we determine how many full boards of a specific length would be required to achieve the total linear meters needed.
Number of Boards (Raw) = Total Linear Meters / Board Length (m)
Step 5: Account for Wastage
It's standard practice to add a percentage for wastage. This accounts for cuts, mistakes, defects in the material, and optimizing board placement.
Total Boards Required = Number of Boards (Raw) * (1 + (Wastage Factor (%) / 100))
The final result is then rounded up to the nearest whole board, as you can't purchase fractions of a board.
Use Cases and Tips
New Deck Construction: The primary use for this calculator is planning materials for a new deck.
Deck Repair/Expansion: If you're replacing a section or adding to an existing deck, ensure your measurements are accurate.
Board Dimensions: Always confirm the exact width and length of the decking boards you plan to purchase, as these can vary by manufacturer and product line.
Gap Consistency: Maintaining a consistent gap is important for both aesthetics and the structural integrity of your deck.
Wastage Factor: A 10% wastage factor is common, but you might increase it for complex deck shapes or if using more intricate patterns.
Units: Ensure all your measurements are consistent. This calculator uses meters for deck dimensions and board length, and millimeters for board and gap width. The internal conversion handles this.
function calculateDeckingBoards() {
var deckLength = parseFloat(document.getElementById("deckLength").value);
var deckWidth = parseFloat(document.getElementById("deckWidth").value);
var boardWidth = parseFloat(document.getElementById("boardWidth").value);
var boardLength = parseFloat(document.getElementById("boardLength").value);
var gapWidth = parseFloat(document.getElementById("gapWidth").value);
var wastageFactor = parseFloat(document.getElementById("wastageFactor").value);
var resultValueElement = document.getElementById("result-value");
var resultUnitElement = document.getElementById("result-unit");
// Clear previous results
resultValueElement.innerText = "0";
resultUnitElement.innerText = "boards";
// Input validation
if (isNaN(deckLength) || deckLength <= 0 ||
isNaN(deckWidth) || deckWidth <= 0 ||
isNaN(boardWidth) || boardWidth <= 0 ||
isNaN(boardLength) || boardLength <= 0 ||
isNaN(gapWidth) || gapWidth < 0 || // Gap can be 0
isNaN(wastageFactor) || wastageFactor < 0) {
alert("Please enter valid positive numbers for all dimensions and wastage factor. Gap width can be 0 or positive.");
return;
}
// Calculations
var deckArea = deckLength * deckWidth; // m²
// Convert mm to meters for usable board width calculation
var usableBoardWidth = (boardWidth + gapWidth) / 1000; // meters
var totalLinearMeters = deckArea / usableBoardWidth; // meters
var numberOfBoardsRaw = totalLinearMeters / boardLength; // count
var totalBoardsRequired = numberOfBoardsRaw * (1 + (wastageFactor / 100)); // count
// Round up to the nearest whole board
var finalBoardCount = Math.ceil(totalBoardsRequired);
resultValueElement.innerText = finalBoardCount;
resultUnitElement.innerText = "boards";
}