Understanding Composite Decking Material and Cost Calculations
Building a composite deck involves careful planning to ensure you have enough material and to accurately estimate the cost. This calculator helps you determine the number of composite boards needed and the total material cost based on your deck's dimensions, the chosen composite board specifications, and your budget.
How the Calculation Works:
The calculator uses a straightforward approach to estimate your composite decking needs:
Deck Area: First, the total square footage of your deck is calculated by multiplying its length by its width.
Deck Area (sq ft) = Deck Length (ft) * Deck Width (ft)
Board Coverage Area: Next, we determine how much area a single composite board covers. Since composite boards are typically sold in standard lengths and their width is measured in inches, we need to convert the board width to feet.
Board Width (ft) = Board Width (inches) / 12 Area per Board (sq ft) = Board Length (ft) * Board Width (ft)
Number of Boards Needed: To find the total number of boards required, we divide the total deck area by the area covered by a single board.
Raw Number of Boards = Deck Area (sq ft) / Area per Board (sq ft)
Accounting for Waste: It's crucial to add a waste factor to account for cuts, mistakes, and unusable pieces. This is applied as a percentage to the raw number of boards.
Total Boards = Raw Number of Boards * (1 + Waste Factor / 100)
The calculator rounds this number up to the nearest whole board, as you cannot purchase fractions of boards.
Total Material Cost: Finally, the total cost is calculated by multiplying the total number of boards by the cost per linear foot of the composite board. Note that the cost is often quoted per linear foot, so we need to consider the length of each board.
Total Cost = Total Boards * Board Length (ft) * Cost per Linear Foot ($)
Example Calculation:
Let's say you have a deck that is 20 feet long and 12 feet wide. You've chosen composite boards that are 5.5 inches wide and 12 feet long. The cost is $4.50 per linear foot, and you're factoring in a 10% waste factor.
Deck Area = 20 ft * 12 ft = 240 sq ft
Board Width = 5.5 inches / 12 = 0.4583 ft
Area per Board = 12 ft * 0.4583 ft = 5.5 sq ft
Raw Number of Boards = 240 sq ft / 5.5 sq ft = 43.64 boards
This calculator provides an estimate. Always consult with your material supplier for precise quantities and consider additional costs for fasteners, framing, labor, and any specialized accessories.
function calculateDecking() {
var deckLength = parseFloat(document.getElementById("deckLength").value);
var deckWidth = parseFloat(document.getElementById("deckWidth").value);
var boardWidthInches = parseFloat(document.getElementById("boardWidth").value);
var boardLengthFeet = parseFloat(document.getElementById("boardLength").value);
var wasteFactor = parseFloat(document.getElementById("wasteFactor").value);
var boardCostPerLinearFoot = parseFloat(document.getElementById("boardCostPerLinearFoot").value);
var resultDiv = document.getElementById("result-value");
resultDiv.innerHTML = ""; // Clear previous results
if (isNaN(deckLength) || isNaN(deckWidth) || isNaN(boardWidthInches) || isNaN(boardLengthFeet) || isNaN(wasteFactor) || isNaN(boardCostPerLinearFoot) ||
deckLength <= 0 || deckWidth <= 0 || boardWidthInches <= 0 || boardLengthFeet <= 0 || wasteFactor < 0 || boardCostPerLinearFoot < 0) {
resultDiv.innerHTML = "Please enter valid positive numbers for all fields.";
return;
}
var deckArea = deckLength * deckWidth;
var boardWidthFeet = boardWidthInches / 12;
var areaPerBoard = boardLengthFeet * boardWidthFeet;
if (areaPerBoard === 0) {
resultDiv.innerHTML = "Board dimensions result in zero area. Please check board width and length.";
return;
}
var rawNumberOfBoards = deckArea / areaPerBoard;
var totalBoardsWithWaste = rawNumberOfBoards * (1 + wasteFactor / 100);
var roundedTotalBoards = Math.ceil(totalBoardsWithWaste);
var totalCost = roundedTotalBoards * boardLengthFeet * boardCostPerLinearFoot;
resultDiv.innerHTML =
"Estimated Boards Needed: " + roundedTotalBoards + "" +
"Estimated Total Cost: $" + totalCost.toFixed(2);
}