Find out exactly how many deck boards you need for your project. Enter deck size, board width and length, gap and waste to get board counts and linear feet.
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This deck board calculator assumes the boards run along the deck length, so the rows stack across the deck width. First it computes the installed width of each board row: the board pitch, equal to the actual board width plus the gap between boards, both in inches. It converts the deck width to inches (feet times 12), divides by the pitch, and rounds up to a whole number of rows. Then it divides the deck length by the board length and rounds up to find how many boards fit end to end in one row. Multiplying rows by boards per row gives the net board count; the waste allowance percentage is applied and the result is rounded up again, because you can only buy whole boards. The final figure, total linear feet, is simply boards needed times board length, which is the number lumber yards price by.
The calculator works with the installed width of each board, not the nominal size on the tag. Add the gap between boards to the actual board width to get the board pitch in inches, which is how much deck width one board plus one gap covers. Convert the deck width from feet to inches (multiply by 12) and divide by the pitch, rounding up to a whole number of rows, because a partial row still needs a full board. Each row runs along the deck length, so boards per row is the deck length divided by the board length, rounded up. Multiply rows by boards per row, multiply by one plus the waste percentage, and round up again: suppliers sell whole boards. Finally, multiply the board count by the board length to get total linear feet for ordering.
Measure your deck with a tape measure in feet: length is the direction the boards will run, width is the direction they stack across. Pick the actual board width your supplier stocks (3.5, 5.5, or 7.25 inches), then the board length (8, 10, 12, or 16 feet). Enter the gap you plan between boards in inches and the waste allowance as a percentage. The deck board calculator updates instantly: rows across the width, boards per row, total boards needed with waste, and total linear feet, whether you are costing a compact 10x10 deck or a large multi-section build. If you plan to run the boards the other way, simply swap the length and width values.
Gaps let water drain, allow boards to expand and contract, and stop moisture from getting trapped between edges. For pressure-treated wood, 1/4 inch is the standard gap; use 1/8 inch if the lumber is kiln-dried and stable, and go wider (3/8 to 1/2 inch) if you are installing wet or green boards that will shrink as they dry. Composite boards usually need 1/8 to 3/16 inch, and you should follow the manufacturer specification for the brand you buy. Small gaps have a bigger effect than they look: a 1/4 inch gap across 26 rows adds more than 6 inches to the total width, so never ignore the gap when counting rows. A 16d nail or a 5/16 inch bolt shank makes a quick, consistent spacer.
Decking is sold by nominal size but measures smaller after milling, and you must calculate with the actual face width. A 5/4x6 or 2x6 board has an actual face of 5.5 inches, the most common decking width. A 2x4 board measures 3.5 inches, and wide composite boards often measure 7.25 inches. Using the nominal 6 inches in your math makes each board look wider than it really is, which underestimates your board count. Stocked lengths are usually 8, 10, 12, 16, and 20 feet. Longer boards mean fewer end joints and a cleaner look, but they are heavier, harder to transport, and some suppliers only stock certain lengths, so choose a length you can actually buy and carry.
Every deck needs extra boards for cuts, notches, and damaged stock, so the waste allowance is part of the calculation, not an afterthought. Add 10 percent for a plain rectangular deck with boards running straight, 15 percent for decks with angles, notches, or boards laid diagonally, and 20 percent for herringbone or complex patterns with lots of short pieces. Add another 5 to 10 percent if your board length does not divide evenly into the deck length, since every run leaves an offcut. It is also wise to keep 2 to 3 extra boards after the build for future repairs, because finding a matching board years later is difficult.
Take a deck 16 feet long and 12 feet wide, built with 5.5 inch boards that are 16 feet long, a 1/8 inch gap, and 10 percent waste. The board pitch is 5.5 + 0.125 = 5.625 inches. Convert the 12 foot width to 144 inches and divide: 144 / 5.625 = 25.6, which rounds up to 26 rows. Boards per row: 16 / 16 = 1, so no end joints. Multiply 26 rows by 1 board per row by 1.10 for waste: 28.6, which rounds up to 29 boards. Total linear feet: 29 × 16 = 464 feet. That is the same math the calculator runs for any deck size and board combination.
Once you know the board count, estimating the material cost is simple arithmetic. Multiply the total boards by the price per board at your supplier, or multiply the total linear feet by the price per linear foot. As a 2026 guide, pressure-treated pine boards run roughly $1.50 to $2.75 per linear foot, cedar and redwood sit in the middle, and composite boards run about $4.50 to $7.00 per linear foot. Board count alone does not give you the full project cost: joists, posts, fasteners, railings and labor typically double or triple the decking-board material total, so get a per-square-foot quote from a local builder for the finished deck building project. Treat all figures here as estimates for planning, not a contractor quote.
For a 12 × 16 ft deck with 5/4x6 boards (5.5 inch face) and a 1/4 inch gap, the pitch is 5.75 inches. Across the 12 ft width (144 inches): 144 / 5.75 = 25.04, so 26 rows. Along the 16 ft length with 16 ft boards, each row needs 1 board. That is 26 boards net, plus 10 percent waste: 26 × 1.10 = 28.6, so order 29 boards. Enter your own numbers in the calculator above for the exact count.
Leave between 1/8 and 1/4 inch between boards for most decks. Pressure-treated lumber usually takes a 1/4 inch gap, or 1/8 inch if it is kiln-dried. Composite decking usually needs 1/8 to 3/16 inch, and you should follow the manufacturer specification. The gap lets water drain and gives boards room to expand; boards laid with no gap trap moisture and rot faster.
Lumber is sold by nominal size, which is what the mill starts with, but arrives milled to a smaller actual size. A nominal 5/4x6 decking board measures 5.5 inches across the face, a 2x6 also measures 5.5 inches wide, and a 2x4 measures 3.5 inches. Always calculate with the actual face width, because using the nominal size makes each board look wider and undercounts the boards you need.
The 5.5 inch wide board (sold as 5/4x6 or 2x6) is the most common choice for residential decks and a safe default. Choose 3.5 inch boards for a tighter, furniture-like look, or 7.25 inch wide composite boards for a bolder pattern with fewer seams. Pick a length your supplier actually stocks; 12 and 16 ft boards are easy to find, 20 ft boards need a long truck and a helper to carry.
Add 10 percent for a plain rectangular deck with boards running straight. Use 15 percent for decks with angles, notches, or a diagonal board pattern, and 20 percent for herringbone or complex layouts. Add another 5 to 10 percent if the board length does not divide evenly into the deck length, since each run leaves an offcut. Keep 2 to 3 extra boards for future repairs.
This calculator assumes the boards run along the deck length, whichever direction you call length. Many builders run boards perpendicular to the house for classic looks and good drainage, while diagonal boards add visual interest but need 15 percent waste. If you plan to run boards the other way, swap the length and width values in the calculator.
Break an L-shaped or irregular deck into separate rectangles, calculate each section on its own, and add the board counts together. Subtract the footprint of built-in features like benches or planters. For curved edges, measure the widest point of each section so you do not come up short. A decking board estimator like this one works best when each rectangle is measured separately.
Plan for about 350 screws per 100 square feet of deck at standard 16 inch joist spacing. The rule is two screws per board at every joist it crosses, or three screws for 2 inch thick boards. Hidden fastener clips are an alternative: figure roughly 2 clips per square foot of deck. Add 10 percent to your fastener count for dropped or stripped screws.
Decking boards themselves are usually the smaller part of the bill: roughly $1.50 to $2.75 per linear foot for pressure-treated pine and about $4.50 to $7.00 per linear foot for composite in 2026 pricing. Multiply your total linear feet by those rates for a material estimate, then add joists, posts, fasteners, railings and labor, which often double or triple the board cost. These are planning estimates, not contractor quotes.
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