Deck Material List Calculator
Understanding Your Deck Material Needs
Building a deck is an exciting home improvement project that adds value and usability to your outdoor space. To ensure a smooth construction process and avoid costly trips to the hardware store, accurate material estimation is crucial. This calculator helps you determine the quantities of key materials needed for your deck's framing and decking, based on your project's dimensions.
How the Calculator Works:
The calculator uses your input dimensions to estimate the number of deck boards, joists, and the total linear feet of lumber required. It also factors in a waste percentage to account for cuts, mistakes, and unusable pieces.
1. Decking Boards:
This calculation estimates the number of linear feet of decking boards needed.
- First, the total area of the deck is calculated:
Area = Deck Length (ft) * Deck Width (ft). - Then, the effective width of a single deck board is determined, considering its nominal width and the gap between boards:
Effective Board Width (ft) = (Board Width (in) + Board Spacing (in)) / 12. - The total linear feet of decking required is then:
Total Decking (ft) = Deck Area (sq ft) / Effective Board Width (ft). - Finally, the waste factor is applied:
Final Decking Needed (ft) = Total Decking (ft) * (1 + Waste Factor (%) / 100).
2. Framing Joists:
Joists run perpendicular to the deck's length and support the decking. They are typically spaced 16 inches or 24 inches on center.
- The number of joist bays is calculated based on the deck's width and joist spacing:
Number of Joist Bays = (Deck Width (ft) * 12 in/ft) / Joist Spacing (in). - The total number of joists needed is typically one more than the number of bays (to account for the joist at the start):
Total Joists = Number of Joist Bays + 1. - Each joist will be the length of the deck's length. Therefore, the total linear footage of lumber for joists is:
Total Joist Lumber (ft) = Total Joists * Deck Length (ft). - The waste factor is applied:
Final Joist Lumber Needed (ft) = Total Joist Lumber (ft) * (1 + Waste Factor (%) / 100).
Example Scenario:
Let's say you're building a deck that is 20 feet long and 12 feet wide. You plan to use standard 5.5-inch wide deck boards with a 0.25-inch gap, and your joists will be spaced 16 inches apart. You've accounted for a 10% waste factor.
- Decking:
- Deck Area = 20 ft * 12 ft = 240 sq ft
- Effective Board Width = (5.5 in + 0.25 in) / 12 = 5.75 in / 12 = 0.479 ft
- Total Decking = 240 sq ft / 0.479 ft = 501.04 linear ft
- Final Decking Needed = 501.04 ft * (1 + 10/100) = 501.04 * 1.1 = 551.14 linear ft
- Framing Joists (assuming joists run the 12ft width):
- Number of Joist Bays = (12 ft * 12 in/ft) / 16 in = 144 in / 16 in = 9 bays
- Total Joists = 9 + 1 = 10 joists
- Total Joist Lumber = 10 joists * 20 ft (deck length) = 200 linear ft
- Final Joist Lumber Needed = 200 ft * (1 + 10/100) = 200 * 1.1 = 220 linear ft
Based on these calculations, you would need approximately 551 linear feet of decking boards and 220 linear feet of lumber for your joists, plus a buffer for waste. You can then use these figures to determine the number of 8ft, 10ft, 12ft, or 16ft boards you need to purchase.
Important Considerations:
- Board Lengths: Standard lumber comes in specific lengths. You'll need to plan your cuts to minimize waste, especially when buying longer boards.
- Joist Direction: This calculator assumes joists run the 'width' of the deck. If your design requires them to run the 'length', you'll need to adjust the joist calculation accordingly.
- Other Materials: This calculator focuses on decking boards and framing joists. You will also need to account for posts, beams, railings, stairs, fasteners (screws, nails), concrete for footings, and potentially concrete form tubes.
- Local Codes: Always check local building codes for specific requirements regarding joist spans, footing depths, and materials.
Please enter valid positive numbers for all inputs (except spacing which can be 0).
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return;
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// — Decking Calculation —
var deckArea = deckLength * deckWidth; // sq ft
// Convert board width and spacing from inches to feet for calculation
var effectiveBoardWidthFt = (boardWidth + boardSpacing) / 12; // ft
var totalDeckingLinearFt = deckArea / effectiveBoardWidthFt; // linear ft
var finalDeckingLinearFt = totalDeckingLinearFt * (1 + wasteFactor / 100);
// Calculate number of boards needed based on common lengths
var boards8ft = Math.ceil(finalDeckingLinearFt / 8);
var boards10ft = Math.ceil(finalDeckingLinearFt / 10);
var boards12ft = Math.ceil(finalDeckingLinearFt / 12);
var boards16ft = Math.ceil(finalDeckingLinearFt / 16);
// — Framing Joists Calculation —
// Assuming joists run along the deck's width dimension
var joistSpanLength = deckLength; // Joists are as long as the deck length
var deckWidthInInches = deckWidth * 12;
var numberOfJoistBays = Math.floor(deckWidthInInches / joistSpacing);
var totalJoists = numberOfJoistBays + 1; // Add one for the start
var totalJoistLinearFt = totalJoists * joistSpanLength;
var finalJoistLinearFt = totalJoistLinearFt * (1 + wasteFactor / 100);
// Display Results
var resultHTML = "Decking Boards: Approx. " + finalDeckingLinearFt.toFixed(2) + " linear feet needed.
";
resultHTML += " – Using 8ft boards: ~" + boards8ft + " boards
";
resultHTML += " – Using 10ft boards: ~" + boards10ft + " boards
";
resultHTML += " – Using 12ft boards: ~" + boards12ft + " boards
";
resultHTML += " – Using 16ft boards: ~" + boards16ft + " boards
";
resultHTML += "Framing Joists (if running parallel to deck width): Approx. " + finalJoistLinearFt.toFixed(2) + " linear feet needed.
";
resultHTML += " – Based on " + joistSpacing + "\" spacing, you'll need approximately " + totalJoists + " joists, each " + joistSpanLength + "ft long.
";
resultDiv.innerHTML = resultHTML;
}