Decking Calculator
Nominal board size — actual width is 0.5 inches less
Stock length to purchase — round up to next even length
Gap between boards in inches (1/8" = 0.125 for wood, 3/16" = 0.1875 for composite)
Auto-set by layout: 10% straight, 15% diagonal, 25% herringbone
Enter Your Deck Dimensions
Enter the deck length, width, board size, and layout options above to get your full material estimate including board count, joists, fasteners, and cost.
How to Use the Decking Calculator
Enter Deck Dimensions
Type in your deck length and width in feet (or meters if using metric mode). For irregular decks, break them into rectangular sections and add the results. These two numbers drive every downstream calculation in the estimator.
Choose Board Size and Layout
Select your nominal board size (2x6, 5/4x6, etc.) and the stock board length you plan to purchase. Pick your layout pattern — 90° straight is most material-efficient. The waste factor updates automatically (10% straight, 15% diagonal, 25% herringbone), but you can override it manually if your site conditions require a different margin.
Set Joist Spacing and Fastener Type
Choose joist spacing based on your decking material: 16" on-center for most wood and composite products on straight runs; 12" on-center for diagonal composite or PVC installations per manufacturer specs. Select screws/nails for face-fastening or hidden clips for a cleaner look — the count formula changes accordingly.
Review Results and Export
Check the material summary for board count, linear footage, joist count, and fastener quantities. Enter optional pricing to see total material cost and cost per square foot. Use the material comparison bars to evaluate pressure-treated vs composite vs PVC costs side-by-side. Export to CSV for a printable shopping list to take to the lumber yard.
Frequently Asked Questions
What is the difference between nominal and actual board width?
Lumber is sold by nominal dimensions that do not reflect the true finished size. A 2x6 board is actually 1.5 inches thick and 5.5 inches wide. A 2x4 is 1.5 x 3.5 inches. The 0.5-inch discrepancy comes from the planing and drying process after the board is rough-sawn. For decking calculations, always use the actual width (nominal minus 0.5 inches) plus your chosen gap to get the true coverage per board row. This calculator applies those conversions automatically based on your board size selection, so the board count is accurate without any manual adjustment on your part.
How much waste should I add for a diagonal deck?
For a straight 90-degree layout, a 10 percent waste factor is standard and accounts for end cuts and occasional defects. A 45-degree diagonal layout should use 15–20 percent waste because every board end requires a miter cut and the triangular off-cuts cannot be reused elsewhere in the deck. Herringbone and V-shaped patterns generate 25–30 percent waste due to the number of angled cuts per board. For picture-frame borders (a straight perimeter band surrounding a diagonal field), calculate the border and field separately and apply different waste rates to each section. This calculator auto-sets the waste factor based on your layout choice, though you can override it for unusual site conditions.
What joist spacing do I need for composite decking?
Most composite and PVC decking manufacturers specify a maximum of 16 inches on-center for straight installations and 12 inches on-center for diagonal installations. This is because composite materials have lower bending stiffness than solid wood and can flex or sag between joists if the spans are too wide. Check the specific manufacturer's installation guide before purchasing — some premium composite products allow 24-inch spacing for straight runs on thicker profiles, while others require 12 inches even for straight layouts. Wood decking (2x6) generally tolerates 24-inch spacing for straight runs, while 5/4x6 wood boards are rated for 16-inch spacing maximum.
How are hidden fastener counts different from screw counts?
Face-screwing uses two screws per board per joist crossing — one on each side of the board going diagonally down into the joist. This creates visible fastener heads on the deck surface. Hidden clip fasteners sit between boards at each joist, engaging a groove routed into the board edge, and require only one clip per board per joist. That means hidden clips typically need about half the quantity of face screws, but each clip costs significantly more ($0.50–$2.00 vs $0.05–$0.15 per screw). Both counts are shown in this calculator so you can evaluate the trade-offs. Note that perimeter boards and border boards still require face screws even in hidden clip systems.
How do I calculate deck area for an L-shaped or irregular deck?
For L-shaped or irregular decks, divide the deck into simple rectangles and calculate each section separately. Add the board counts from each section together, then apply a single combined waste factor. Alternatively, if you are using this calculator and your deck has multiple sections, run the calculation once for each rectangular section and sum the totals. For sections that share a board run (one board spans two sections), treat them as a single rectangle for board count purposes. The linear footage and board footage outputs can be summed directly. For complex decks with angles and cutouts, add 5 percent extra to your waste factor to account for the additional cuts at boundaries.
What is board footage (BF) and why does it matter for ordering lumber?
Board footage is a volume-based unit of lumber measurement equal to a board 1 inch thick, 12 inches wide, and 12 inches long. The formula is: BF = (nominal thickness × nominal width × length in feet) / 12. For example, a 2x6 that is 16 feet long contains (2 × 6 × 16) / 12 = 16 board feet. Lumber yards often price hardwoods and some specialty softwoods by the board foot rather than by the linear foot or piece. When ordering Ipe, Tigerwood, or other exotic hardwoods, you will typically need to specify total board footage. This calculator outputs both linear footage (for standard pricing) and board footage (for hardwood and specialty lumber ordering) so you are prepared for either pricing model at the supplier.