Decking Calculator
ConstructionCalculate how many deck boards and total linear feet of decking you need for a rectangular deck, including a wastage allowance for cuts and offcuts.
Number of Boards
27
Total Linear Feet
476
What is a Decking?
A Decking Calculator determines how many deck boards and total linear feet of decking material you need to cover a rectangular deck, including an allowance for cuts and waste. Whether you're building with pressure-treated lumber or composite decking, ordering the right quantity upfront avoids both costly mid-project material runs and excess leftover boards.
This tool takes your deck length, deck width, board width, and wastage percentage to calculate both the number of boards spanning the deck's width and the total linear feet of material to order. If your deck project includes a railing, the Baluster Calculator can help you plan that layout, and the Square Footage Calculator is useful for irregular deck shapes.
How to use this Decking calculator
- Enter your Deck Length in feet.
- Enter your Deck Width in feet.
- Enter the Board Width in inches — 5.5 inches is the standard default for a nominal 1x6 board.
- Set your Wastage percentage to account for cuts and offcuts — 10% is a reasonable default for a standard rectangular deck.
- Review the Number of Boards result to see how many boards span your deck's width.
- Check the Total Linear Feet result, which is the figure to use when ordering material from a lumberyard.
- Adjust any input to instantly recalculate — useful for comparing different board widths or wastage assumptions before finalizing your order.
Formula & Methodology
The calculator uses the following steps: Number of Boards = ceil((Deck Width × 12) ÷ Board Width) Total Linear Feet = ceil(Number of Boards × Deck Length × (1 + Wastage %)) Worked example: For a 16-foot by 12-foot deck, using 5.5-inch wide boards with 10% wastage: Number of Boards = ceil((12 × 12) ÷ 5.5) = ceil(144 ÷ 5.5) = ceil(26.18) = 27 boards Total Linear Feet = ceil(27 × 16 × 1.10) = ceil(475.2) = 476 linear feet This gives you a material order of 476 total linear feet of decking, spread across 27 boards running the width of the deck.
Frequently Asked Questions
The calculator divides your deck width by the board width to determine how many boards are needed to span across the deck, then multiplies that count by the deck length and adds your wastage percentage to get the total linear feet of decking material to order. This two-step process accounts for both the layout across the deck and the total lumber length required.
The most common deck board width in the US is 5.5 inches (the actual width of a nominal 1x6 board), which this calculator uses as its default. Other common widths include 3.5 inches (1x4) and various composite decking widths, which typically range from 5.25 to 5.5 inches depending on the manufacturer.
Number of Boards is calculated as the ceiling of (Deck Width in inches ÷ Board Width). Total Linear Feet is then calculated as the ceiling of (Number of Boards × Deck Length × (1 + Wastage %)). This gives you both a board count for layout purposes and a total lumber quantity for ordering.
A wastage allowance of 10 percent is standard for most rectangular deck layouts, covering end cuts, angled cuts around posts, and occasional defective boards. Decks with diagonal board patterns, curved edges, or many obstructions like posts and stairs may need a higher allowance of 15 percent or more. This calculator lets you adjust the Wastage input to match your specific deck design.
No, this calculator estimates board count based on board width alone and does not add extra spacing for expansion gaps between boards. Since gap spacing is typically small (around 1/8 to 3/16 inch) and varies by decking material, most builders account for it within their standard wastage percentage rather than as a separate input.
Wood decking, typically pressure-treated pine or cedar, is generally less expensive upfront but requires more maintenance like staining and sealing. Composite decking, made from a blend of wood fibers and plastic, costs more initially but requires little to no ongoing maintenance and resists rot and splintering. This calculator works for either material — just enter the correct board width for your chosen product.
For a 16-foot by 12-foot deck using standard 5.5-inch wide boards with 10% wastage, the calculator returns 27 boards across the width and 476 total linear feet of decking material. You can verify this yourself by entering those values into the calculator above. Your specific result will vary based on your deck's exact dimensions and board width.
This calculator assumes boards run across the Deck Width (parallel to the Deck Length), which is the most common layout for rectangular decks. If you plan to run boards the other direction, simply swap your Deck Length and Deck Width values when entering them into the calculator to get an accurate board count for your specific layout.
Yes, the board and linear footage math is the same whether you're building a brand-new deck frame or simply resurfacing an existing deck structure with new boards. Just measure your deck's actual surface dimensions and enter them into the calculator. If you also need to plan a railing for the deck, the [Baluster Calculator](/baluster-calculator/) can help with that part of the project.
Beyond board count, you may also want the [Baluster Calculator](/baluster-calculator/) for railing spacing, the [Square Footage Calculator](/square-footage-calculator/) for measuring irregular deck shapes, and the [Concrete Calculator](/concrete-calculator/) if you're pouring footings for deck posts. Using these tools together gives you a complete material estimate before you start ordering lumber and concrete.
Divide the Total Linear Feet result by the standard board length sold at your lumberyard (commonly 8, 12, 16, or 20 feet) and round up to the nearest whole board. For example, if your project needs 476 linear feet and boards are sold in 16-foot lengths, you'd need to purchase 30 boards (476 ÷ 16 = 29.75, rounded up).
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