Deck Calculator
Enter your deck dimensions and board specifications to find out how many boards and screws you need along with the estimated cost. Add stairs for a complete material list.
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Planning Your Deck Materials
A successful deck project starts with accurate material estimates. Too few boards mean a frustrating mid-project trip to the store. Too many mean wasted money on returns or leftover lumber taking up garage space. This calculator helps you find the sweet spot.
The board count depends on three numbers: deck width, deck length, and individual board dimensions. Standard 5.5-inch wide boards laid perpendicular to the joists create the classic deck surface. Wider boards reduce the number of rows but may cost more per board.
Do not forget that board length matters for waste. If your deck is 14 feet long and you buy 12-foot boards, every row needs two boards with 10 feet of combined waste. Buying 16-foot boards eliminates the splice and reduces waste to just 2 feet per row.
Wood vs. Composite Deck Boards
Pressure-treated lumber is the most affordable option, typically running 2 to 4 dollars per linear foot. It resists rot and insects but requires annual staining or sealing to maintain its appearance. Expect it to last 15 to 25 years with proper maintenance.
Composite decking costs 4 to 10 dollars per linear foot but needs almost no maintenance beyond occasional cleaning. It does not splinter, warp, or rot. Most manufacturers offer 25-year or even lifetime warranties against structural defects and staining.
Cedar and redwood fall between the two in price and maintenance. They have natural rot resistance and a warm appearance but still benefit from periodic sealing. Hardwoods like ipe are the most durable and expensive, lasting 40 years or more with minimal care.
Accounting for Stairs and Railing
Stairs add complexity to a deck estimate. Each step typically uses two treads (5.5-inch boards) and a pair of stringer boards on each side. The stair width determines how many boards span each step. A 3-foot-wide staircase is the most common residential size.
Railings are required by code for decks 30 inches or more above grade. A standard railing system includes posts every 6 to 8 feet, a top rail, bottom rail, and balusters spaced no more than 4 inches apart. Pre-made railing kits simplify the material list.
For a complete budget, add the stair and railing materials to your decking board cost. Stairs and railings can add 20 to 30 percent to the overall project cost depending on the materials chosen and the height of the deck above ground level.
Frequently Asked Questions
How does the board count work?
The calculator divides the deck width by the board width to find the number of rows, then divides the deck length by the board length to find boards per row. It rounds up both values because partial boards require a full board purchase.
Why 2.5 screws per square foot?
Deck screws are typically placed every 16 inches along each joist. With joists spaced 16 inches apart, you end up using roughly 2 to 3 screws per square foot of decking. The 2.5 average accounts for standard joist spacing.
Should I add extra boards for waste?
Yes. Add 10 to 15 percent to the board count for cutting waste, especially if your deck has angles or the boards do not divide evenly into the deck length. This calculator gives the theoretical minimum before waste.
What about substructure materials?
This calculator covers decking boards only. You will also need joists, beams, posts, post anchors, joist hangers, and hardware. For the substructure, consult a deck framing guide or builder for your specific design.
What is the most common deck board size?
The most common deck board is a nominal 2-by-6, which actually measures 1.5 by 5.5 inches. Composite boards also come in 5.5-inch widths. Some premium products use 5.36-inch or 7.25-inch boards.