Deck Boards Calculator
Enter your deck dimensions, board size, and installation pattern to get an accurate board count, linear footage, and square footage — waste factor included.
1Deck Dimensions
Direction boards run across
Direction boards span
2Board Settings
Choose the longest board that minimizes splices
Wet/green lumber should be installed tight — it will shrink to 1/4" as it dries
Picture frame border runs perpendicular to field boards
Your Deck Board Estimate
Layout Summary
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Tip: Buy boards in the longest length available that works for your deck span. Fewer splices means a cleaner look and stronger deck. A 20 ft deck should use 20 ft boards not two 10 ft boards spliced mid-span.
How to Use This Calculator
To ensure you buy the exact amount of lumber needed without excessive waste, follow these five steps using our deck boards calculator:
- 1Measure your deck dimensions. The "length" is the direction the decking boards will physically run across, while the "width" is the total span each board covers from edge to edge. Determine these in feet and inches.
- 2Select the board size. The 5/4x6 board is the most common decking material used in residential construction. Remember that "nominal" lumber sizes are not exact; a 6-inch board actually measures exactly 5.5 inches wide.
- 3Select the board length. Buying the longest board that can span your entire deck structure without needing to splice two pieces together provides a much cleaner, more professional look.
- 4Choose your gap spacing. Wet, heavy pressure-treated lumber should be installed completely tight with no gap; as the moisture bakes out in the sun, the wood will shrink and naturally create a perfect 1/4 inch gap. Dry lumber requires manual spacing.
- 5Choose your pattern. Select whether you are running the boards straight or diagonal, and choose whether to frame the perimeter with a decorative picture frame border.
The Formula
This deck boards calculator utilizes standard construction geometry to determine your exact material needs. Here is the math behind the scenes in plain English:
Effective Width = (Actual Board Width + Gap Width) / 12
Total Rows = Deck Length / Effective Width (Rounded Up)
Linear Feet = Rows × Deck Width × Number of Sections
Total With Waste = Linear Feet × 1.10 (or 1.15 for diagonal)
Boards Needed = Total With Waste / Board Length (Rounded Up)
First, the calculator must determine the "effective width" of a single board. It does this by adding the actual physical width of the board in inches to the gap size in inches, and then converting that number into feet. Next, it divides your deck's overall length by that effective width to find exactly how many horizontal rows of decking you need.
To find the total linear feet of lumber required, the number of rows is multiplied by the deck's width and the total number of identical deck sections. Because construction always yields cutoffs and scraps, a strict waste factor is applied: 10% for straight patterns and 15% for diagonal layouts. The final linear footage is divided by your selected board length to give you the exact number of boards to purchase. If a picture frame border is selected, the outer perimeter is calculated, multiplied by the number of border layers, multiplied by a 1.10 corner waste factor, and converted into extra boards.
Frequently Asked Questions
Should I use 5/4x6 or 2x6 decking?
The 5/4x6 board (actual thickness 1 inch) is the industry standard. It is lighter, cheaper, and features rounded radius edges for a finished look. A standard 2x6 board (actual thickness 1.5 inches) is significantly stronger, holds up better against cupping, and can span 24-inch joist spacing, but it is heavier, more expensive, and usually has square edges.
What gap should I leave between deck boards for pressure treated versus composite?
If installing green or wet pressure-treated lumber, install the boards tight against each other with zero gap. As the wet wood dries, it will naturally shrink and create a perfect 1/4 inch gap. If the wood is kiln-dried, manually leave a 1/8 to 1/4 inch gap. For composite decking, always follow the manufacturer's exact specifications, though many require hidden fasteners that automatically dictate a 3/16 inch gap.
Does diagonal decking require more boards?
Yes. Installing deck boards on a 45-degree diagonal requires roughly 15% more material than a standard straight layout. Every board that hits the edge of the deck must be cut at an angle, creating significantly more cutoff waste. You will see this difference instantly when toggling the pattern setting in the deck boards calculator.
How do I handle splices where a board is not long enough to span the full deck?
Whenever possible, buy boards long enough to span the entire deck to eliminate splices. If your deck spans 20 feet and you must use shorter boards, ensure every single splice lands perfectly centered over a joist. You must also stagger your joints so they do not line up on the same joist in adjacent rows.
Should I pre-drill deck boards to prevent splitting?
Yes, it is highly recommended to pre-drill your screw holes, especially when driving fasteners within 2 inches of the end of a board. Pre-drilling significantly reduces the risk of the wood splitting and cracking over time.
How many deck screws do I need per board?
You will need two screws at every joist intersection. For a standard deck with joists spaced 16 inches on center, you can estimate roughly 3.5 screws per square foot of decking. For a 16-foot board, you will use approximately 26 screws.