Deck Building Lumber Calculator

Estimate the lumber needed for your deck project, including decking, joists, beams, and posts. This calculator helps you plan your material purchases more accurately, reducing waste and saving time.

Deck Dimensions

Deck Length (feet):
Deck Width (feet):

Decking Boards

Decking Board Width (inches, e.g., 5.5 for 2×6):
Decking Board Length (feet, e.g., 12, 16):
Decking Waste Factor (%):

Joists

Joist Spacing (inches on center, e.g., 16):
Joist Board Length (feet, e.g., 10, 12):
Joist Waste Factor (%):

Beams

Beam Spacing (feet on center, e.g., 8):
Beam Board Length (feet, e.g., 12, 16):
Number of Plies per Beam (e.g., 2 for double):
Beam Waste Factor (%):

Posts

Post Spacing along Beam (feet on center, e.g., 6):
Post Height (feet, e.g., 8, 10):
Post Waste Factor (%):

Estimated Lumber Needed

Fill in the details and click "Calculate Lumber" to see your estimates.

function calculateLumber() { // 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 deckingWaste = parseFloat(document.getElementById("deckingWaste").value) / 100; var joistSpacing = parseFloat(document.getElementById("joistSpacing").value); var joistLength = parseFloat(document.getElementById("joistLength").value); var joistWaste = parseFloat(document.getElementById("joistWaste").value) / 100; var beamSpacing = parseFloat(document.getElementById("beamSpacing").value); var beamLength = parseFloat(document.getElementById("beamLength").value); var beamPlies = parseFloat(document.getElementById("beamPlies").value); var beamWaste = parseFloat(document.getElementById("beamWaste").value) / 100; var postSpacing = parseFloat(document.getElementById("postSpacing").value); var postHeight = parseFloat(document.getElementById("postHeight").value); var postWaste = parseFloat(document.getElementById("postWaste").value) / 100; // Validate inputs if (isNaN(deckLength) || isNaN(deckWidth) || isNaN(deckingBoardWidth) || isNaN(deckingBoardLength) || isNaN(deckingWaste) || isNaN(joistSpacing) || isNaN(joistLength) || isNaN(joistWaste) || isNaN(beamSpacing) || isNaN(beamLength) || isNaN(beamPlies) || isNaN(beamWaste) || isNaN(postSpacing) || isNaN(postHeight) || isNaN(postWaste) || deckLength <= 0 || deckWidth <= 0 || deckingBoardWidth <= 0 || deckingBoardLength <= 0 || joistSpacing <= 0 || joistLength <= 0 || beamSpacing <= 0 || beamLength <= 0 || beamPlies <= 0 || postSpacing <= 0 || postHeight <= 0) { document.getElementById("result").innerHTML = "Please enter valid positive numbers for all fields."; return; } // — Decking Calculation — // Assuming decking boards run parallel to the deckLength, covering the deckWidth var numDeckingBoardsAcrossWidth = Math.ceil((deckWidth * 12) / deckingBoardWidth); var totalLinearFeetDecking = numDeckingBoardsAcrossWidth * deckLength; var totalLinearFeetDeckingWithWaste = totalLinearFeetDecking * (1 + deckingWaste); var numDeckingBoards = Math.ceil(totalLinearFeetDeckingWithWaste / deckingBoardLength); // — Joist Calculation — // Assuming joists run parallel to the deckWidth, covering the deckLength var numJoists = Math.ceil((deckLength * 12) / joistSpacing) + 1; // +1 for the end joist var totalLinearFeetJoists = numJoists * joistLength; var totalLinearFeetJoistsWithWaste = totalLinearFeetJoists * (1 + joistWaste); var numJoistBoards = Math.ceil(totalLinearFeetJoistsWithWaste / joistLength); // — Beam Calculation — // Assuming beams run parallel to the deckLength, supporting the joists // We calculate the number of free-standing beams (excluding the ledger attached to the house) var numFreeStandingBeams = Math.floor(deckWidth / beamSpacing); var totalLinearFeetBeams = numFreeStandingBeams * beamLength * beamPlies; var totalLinearFeetBeamsWithWaste = totalLinearFeetBeams * (1 + beamWaste); var numBeamBoards = Math.ceil(totalLinearFeetBeamsWithWaste / beamLength); // — Post Calculation — // Posts support the free-standing beams var numPostsPerBeam = Math.ceil(beamLength / postSpacing) + 1; // +1 for the end post var totalPosts = numFreeStandingBeams * numPostsPerBeam; var totalLinearFeetPosts = totalPosts * postHeight; var totalLinearFeetPostsWithWaste = totalLinearFeetPosts * (1 + postWaste); var numPostBoards = Math.ceil(totalLinearFeetPostsWithWaste / postHeight); // Display results var resultHtml = "

Decking:

"; resultHtml += "Total Decking Boards: " + numDeckingBoards + " boards (each " + deckingBoardLength + " ft long)"; resultHtml += "Total Linear Feet of Decking: " + totalLinearFeetDeckingWithWaste.toFixed(2) + " linear feet"; resultHtml += "

Joists:

"; resultHtml += "Total Joists: " + numJoistBoards + " boards (each " + joistLength + " ft long)"; resultHtml += "Total Linear Feet of Joists: " + totalLinearFeetJoistsWithWaste.toFixed(2) + " linear feet"; resultHtml += "

Beams:

"; resultHtml += "Total Beam Boards: " + numBeamBoards + " boards (each " + beamLength + " ft long, for " + numFreeStandingBeams + " free-standing beams)"; resultHtml += "Total Linear Feet of Beams: " + totalLinearFeetBeamsWithWaste.toFixed(2) + " linear feet"; resultHtml += "

Posts:

"; resultHtml += "Total Posts: " + numPostBoards + " posts (each " + postHeight + " ft high)"; resultHtml += "Total Linear Feet of Posts: " + totalLinearFeetPostsWithWaste.toFixed(2) + " linear feet"; document.getElementById("result").innerHTML = resultHtml; } .calculator-container { font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif; background-color: #f9f9f9; padding: 25px; border-radius: 10px; box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1); max-width: 700px; margin: 20px auto; border: 1px solid #e0e0e0; } .calculator-container h2 { color: #2c3e50; text-align: center; margin-bottom: 20px; font-size: 1.8em; } .calculator-container h3 { color: #34495e; margin-top: 25px; margin-bottom: 15px; font-size: 1.3em; border-bottom: 1px solid #eee; padding-bottom: 5px; } .calculator-container p { color: #555; line-height: 1.6; margin-bottom: 10px; } .calculator-inputs label { display: block; margin-bottom: 8px; color: #333; font-weight: bold; font-size: 0.95em; } .calculator-inputs input[type="number"] { width: calc(100% – 22px); padding: 10px; margin-bottom: 15px; border: 1px solid #ccc; border-radius: 5px; font-size: 1em; box-sizing: border-box; } .calculator-inputs input[type="number"]:focus { border-color: #007bff; box-shadow: 0 0 5px rgba(0, 123, 255, 0.3); outline: none; } .calculator-inputs button { background-color: #28a745; color: white; padding: 12px 25px; border: none; border-radius: 5px; cursor: pointer; font-size: 1.1em; margin-top: 20px; display: block; width: 100%; transition: background-color 0.3s ease; } .calculator-inputs button:hover { background-color: #218838; } .calculator-results { background-color: #e9f7ef; padding: 20px; border-radius: 8px; margin-top: 30px; border: 1px solid #d4edda; } .calculator-results h3 { color: #28a745; text-align: center; margin-bottom: 15px; font-size: 1.5em; } .calculator-results h4 { color: #34495e; margin-top: 20px; margin-bottom: 10px; font-size: 1.1em; border-bottom: 1px dashed #c3e6cb; padding-bottom: 5px; } .calculator-results p { font-size: 1em; color: #333; margin-bottom: 8px; } .calculator-results p strong { color: #0056b3; }

Understanding Your Deck Building Lumber Needs

Building a deck is a rewarding home improvement project that adds outdoor living space and increases property value. However, accurately estimating the lumber required can be a complex task. Our Deck Building Lumber Calculator simplifies this process, helping you determine the quantities of decking, joists, beams, and posts you'll need, minimizing waste and ensuring you stay within budget.

Why Use a Deck Building Lumber Calculator?

Accurate Budgeting: Lumber costs can be a significant portion of your deck project. Precise estimates help you set a realistic budget and avoid unexpected expenses.
Reduced Waste: Over-ordering materials leads to unnecessary costs and disposal challenges. Under-ordering causes delays and extra trips to the lumber yard. A calculator helps you get it just right.
Efficient Planning: Knowing your material list in advance allows for smoother project execution, from ordering to delivery and construction.
Component Breakdown: The calculator breaks down lumber needs by component (decking, joists, beams, posts), giving you a clear understanding of each part of your deck's structure.

How to Use the Calculator

To get the most accurate estimate, gather the following information about your planned deck:

Deck Length & Width (feet): The overall dimensions of your deck.
Decking Board Width (inches): The actual width of the decking boards you plan to use (e.g., a nominal 2×6 board is typically 5.5 inches wide).
Decking Board Length (feet): The standard lengths of decking boards available at your supplier (e.g., 12 ft, 16 ft).
Joist Spacing (inches on center): The distance between the center of one joist and the center of the next (common values are 12″, 16″, or 24″).
Joist Board Length (feet): The length of the joist boards you'll purchase. This typically corresponds to the deck's width, plus any overhang.
Beam Spacing (feet on center): The distance between your main support beams. This influences the span of your joists.
Beam Board Length (feet): The length of the boards used to construct your beams. This usually corresponds to the deck's length.
Number of Plies per Beam: How many individual boards will be laminated together to form each beam (e.g., a "double 2×10" beam uses two 2×10 boards).
Post Spacing along Beam (feet on center): The distance between the posts supporting each beam.
Post Height (feet): The desired height of your support posts.
Waste Factor (%): An essential input to account for cuts, mistakes, and damaged pieces. A typical waste factor is 10-15%, but it can vary based on your experience and deck complexity.

Understanding Deck Components

Decking: These are the boards that form the walking surface of your deck. They are typically laid perpendicular to the joists.
Joists: These are the horizontal framing members that support the decking. They transfer the load from the decking to the beams.
Beams: Larger horizontal members that support the joists. Beams are typically made by laminating two or more boards together for increased strength.
Posts: Vertical members that support the beams, transferring the deck's weight down to the footings.

Tips for Accurate Estimation

Check Local Building Codes: Always consult your local building codes for specific requirements regarding joist spacing, beam sizing, post dimensions, and footing requirements. These codes dictate structural integrity and safety.
Consider Lumber Dimensions: Remember that nominal lumber sizes (e.g., 2×6, 2×8) are different from actual dimensions (e.g., 1.5″ x 5.5″, 1.5″ x 7.25″). Use the actual dimensions for calculations.
Standard Lumber Lengths: Lumber is typically sold in even-numbered lengths (e.g., 8, 10, 12, 14, 16, 20 feet). Plan your cuts to minimize waste from these standard lengths.
Account for Overhangs: If your decking or joists will overhang the main structure, ensure your board lengths account for this.
Stairs and Railings: This calculator focuses on the main deck structure. Remember to budget separately for stair stringers, treads, railing posts, balusters, and handrails.
Fasteners and Hardware: Don't forget to include screws, nails, joist hangers, post bases, and other hardware in your overall project budget.

By using this calculator and following these guidelines, you'll be well on your way to a successful deck building project!