Use this calculator to estimate the quantity of materials needed for your deck project. Input your deck dimensions and material specifications to get an approximate material list.
Deck Dimensions
Decking Boards
Joists (Under Decking)
Beams (Supporting Joists)
Posts (Supporting Beams)
Footings (For Posts)
Waste Factor
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function calculateDeckMaterials() {
// Get input values
var deckLength = parseFloat(document.getElementById('deckLength').value);
var deckWidth = parseFloat(document.getElementById('deckWidth').value);
var deckingBoardWidth = parseFloat(document.getElementById('deckingBoardWidth').value);
var deckingBoardLength = parseFloat(document.getElementById('deckingBoardLength').value);
var deckingBoardGap = parseFloat(document.getElementById('deckingBoardGap').value);
var joistSpacing = parseFloat(document.getElementById('joistSpacing').value);
var joistLength = parseFloat(document.getElementById('joistLength').value);
var beamSpacing = parseFloat(document.getElementById('beamSpacing').value);
var beamLength = parseFloat(document.getElementById('beamLength').value);
var postSpacing = parseFloat(document.getElementById('postSpacing').value);
var postHeight = parseFloat(document.getElementById('postHeight').value);
var footingDiameter = parseFloat(document.getElementById('footingDiameter').value);
var footingDepth = parseFloat(document.getElementById('footingDepth').value);
var wasteFactor = parseFloat(document.getElementById('wasteFactor').value);
// Validate inputs
if (isNaN(deckLength) || isNaN(deckWidth) || isNaN(deckingBoardWidth) || isNaN(deckingBoardLength) || isNaN(deckingBoardGap) ||
isNaN(joistSpacing) || isNaN(joistLength) || isNaN(beamSpacing) || isNaN(beamLength) ||
isNaN(postSpacing) || isNaN(postHeight) || isNaN(footingDiameter) || isNaN(footingDepth) || isNaN(wasteFactor) ||
deckLength <= 0 || deckWidth <= 0 || deckingBoardWidth <= 0 || deckingBoardLength <= 0 || deckingBoardGap < 0 ||
joistSpacing <= 0 || joistLength <= 0 || beamSpacing <= 0 || beamLength <= 0 ||
postSpacing <= 0 || postHeight <= 0 || footingDiameter <= 0 || footingDepth <= 0 || wasteFactor < 0) {
document.getElementById('result').innerHTML = 'Please enter valid positive numbers for all fields.';
return;
}
// Convert waste factor to a decimal
var actualWasteFactor = wasteFactor / 100;
// 1. Decking Boards
// Calculate number of boards needed across the width
var numDeckingBoardsAcross = (deckWidth * 12) / (deckingBoardWidth + deckingBoardGap);
var totalLinearFeetDecking = numDeckingBoardsAcross * deckLength;
var numIndividualDeckingBoards = Math.ceil(totalLinearFeetDecking / deckingBoardLength);
var numIndividualDeckingBoardsWithWaste = Math.ceil(numIndividualDeckingBoards * (1 + actualWasteFactor));
// 2. Joists (assuming joists run the shorter dimension, typically width, and are supported by beams)
// Number of joists depends on deck length and joist spacing
var numJoists = Math.ceil((deckLength * 12) / joistSpacing) + 1; // +1 for the end joist
var totalLinearFeetJoists = numJoists * deckWidth;
var numIndividualJoists = Math.ceil(totalLinearFeetJoists / joistLength);
var numIndividualJoistsWithWaste = Math.ceil(numIndividualJoists * (1 + actualWasteFactor));
// 3. Beams (assuming beams run the longer dimension, typically length, and support joists)
// Number of beams depends on deck width and beam spacing
var numBeams = Math.ceil((deckWidth * 12) / (beamSpacing * 12)) + 1; // +1 for the end beam
var totalLinearFeetBeams = numBeams * deckLength;
var numIndividualBeams = Math.ceil(totalLinearFeetBeams / beamLength);
var numIndividualBeamsWithWaste = Math.ceil(numIndividualBeams * (1 + actualWasteFactor));
// 4. Posts (supporting beams)
// Number of posts per beam depends on deck length and post spacing
var numPostsPerBeam = Math.ceil(deckLength / postSpacing) + 1; // +1 for the end post
var totalPosts = numPostsPerBeam * numBeams;
var totalLinearFeetPosts = totalPosts * postHeight;
var numIndividualPosts = Math.ceil(totalLinearFeetPosts / postHeight); // Assuming posts are bought in their required height
var numIndividualPostsWithWaste = Math.ceil(numIndividualPosts * (1 + actualWasteFactor));
// 5. Concrete for Footings
var footingRadiusFeet = (footingDiameter / 2) / 12; // Convert inches to feet
var footingDepthFeet = footingDepth / 12; // Convert inches to feet
var volumeOneFootingCubicFeet = Math.PI * Math.pow(footingRadiusFeet, 2) * footingDepthFeet;
var totalConcreteVolumeCubicFeet = volumeOneFootingCubicFeet * totalPosts;
// Approximate 80lb bag of concrete yields about 0.6 cubic feet
var bags80lbConcrete = Math.ceil(totalConcreteVolumeCubicFeet / 0.6);
// Display results
var resultHtml = '
Building a deck is a rewarding home improvement project that adds valuable outdoor living space. However, accurately estimating the materials needed can be a complex task. Our Deck Material Calculator simplifies this process, providing you with a clear estimate for the essential components of your deck.
Why Use a Deck Material Calculator?
Budgeting: Get a realistic idea of material costs before you start, helping you stay within your budget.
Efficiency: Avoid over-ordering or under-ordering materials, saving time and reducing waste.
Planning: Understand the quantities of each component, which aids in project planning and logistics.
Accuracy: While an estimate, it provides a much more accurate starting point than guesswork.
Key Deck Components Explained:
1. Decking Boards
These are the visible surface boards you walk on. They come in various materials like treated lumber, cedar, redwood, or composite. The calculator asks for their width and standard length, along with the gap you plan to leave between them for drainage and expansion. The calculation determines how many boards you'll need to cover the entire deck surface.
Example: For a 12ft x 10ft deck using 5.5-inch wide boards with a 1/4-inch gap, you might need around 24 boards of 12ft length, accounting for waste.
2. Joists
Joists are the horizontal framing members that support the decking boards. They typically run perpendicular to the decking and are spaced at regular intervals (e.g., 16 inches on center) to provide adequate support. The calculator estimates the number of joists based on your deck's length and the specified joist spacing, assuming they span the deck's width.
Example: A 12ft x 10ft deck with joists spaced 16 inches on center along the 12ft length would require approximately 10 joists, each 10ft long (or standard 12ft lengths cut down).
3. Beams
Beams are larger structural members that run perpendicular to the joists and support them. They transfer the deck's load to the posts. The calculator determines the number of beams based on your deck's width and the beam spacing, assuming they span the deck's length.
Example: For a 12ft x 10ft deck with beams spaced 8 feet apart along the 10ft width, you would need about 3 beams, each 12ft long.
4. Posts
Posts are the vertical supports that hold up the beams and, consequently, the entire deck structure. They are typically anchored in concrete footings. The calculator estimates the number of posts required based on the number of beams and the post spacing along each beam, as well as their required height.
Example: If you have 3 beams, and each beam requires posts every 8 feet along its 12ft length, you would need about 3 posts per beam, totaling 9 posts.
5. Concrete for Footings
Footings are the concrete bases that provide a stable foundation for your deck posts, preventing settling and uplift. The calculator estimates the total volume of concrete needed based on the number of posts, and the specified diameter and depth of each footing. This volume is then converted into the approximate number of 80lb bags of concrete mix you'll need.
Example: For 9 posts, each with a 10-inch diameter and 24-inch deep footing, you might need around 17 x 80lb bags of concrete.
Waste Factor
It's crucial to include a waste factor in your material estimates. This accounts for cuts, mistakes, damaged pieces, and future repairs. A typical waste factor for deck projects is 10-15%, but it can vary depending on your skill level and the complexity of the deck design.
Important Considerations:
Local Building Codes: Always check with your local building department for specific requirements regarding deck construction, including joist/beam/post sizing, spacing, and footing depth. These codes can vary significantly by region.
Material Sizing: The calculator assumes standard board lengths. You may need to adjust your purchase based on available lengths at your local lumberyard to minimize waste.
Fasteners and Hardware: This calculator focuses on major lumber and concrete components. Remember to budget for deck screws, joist hangers, post bases, bolts, and other necessary hardware.
Railing and Stairs: If your deck includes railings or stairs, these will require additional material calculations not covered by this basic calculator.
This calculator provides a helpful starting point for your deck project. For precise planning and safety, always consult with a qualified builder or engineer.