Free construction tool
Decking calculator
Deck boards, linear feet, joists, and screws from your deck length and width. Pick wood (16 inch on-center) or composite (12 inch on-center), set straight or diagonal waste, and price the boards per linear foot. The formula prints under the results so you can check the math.
A 16' x 12' deck is 192 SF. Boards run the 16' length, so rows across the 12' width = ceil(12 x 12 / 5.75) = 26 rows. Board linear feet = 26 rows x 16' x 1.08 waste = 449.28 LF, so at 16' stock you buy 29 boards. Joists at Wood (16" OC) = ceil(12 x 12 / 16) + 1 = 10. Screws = 192 SF x 3.5 = 672.
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What a decking takeoff counts
A deck is four counts off one rectangle. Give the calculator the deck length and width in feet and it returns the deck boards (as a count and as total linear feet), the joists at your chosen spacing, the screws, and the decking cost. Boards run the long way, joists run across underneath them, and everything scales off the surface area. Get those four numbers right and the material order writes itself.
The formulas, with a worked example
Take a 16 ft by 12 ft deck (192 square feet). Boards run the 16 ft length, so you count rows across the 12 ft width. A standard board has a 5.5 inch face and you leave a 1/4 inch drainage gap, so each row eats 5.75 inches: rows = ceil(12 x 12 / 5.75) = ceil(25.04) = 26 rows. Board linear feet = 26 rows x 16 ft x 1.08 for 8 percent straight waste = 449.28 LF. At 16 ft stock that is ceil(449.28 / 16) = 29 boards. Joists at 16 inch on-center = ceil(12 x 12 / 16) + 1 = 10. Screws at 3.5 per square foot = 192 x 3.5 = 672.
Joist spacing: wood versus composite
Wood decking is framed at 16 inch on-center by default. Composite boards are less stiff and sag between joists set that far apart, so most composite manufacturers require 12 inch on-center for perpendicular runs (and 8 to 10 inch for a diagonal pattern). Tighter spacing means more joists: the same 12 ft width goes from 10 joists at 16 inch to 13 at 12 inch. Always check the specific board's span table, because the warranty depends on it.
Board face, gaps, and waste
The 5.75 inch row pitch assumes a 5.5 inch board with a 1/4 inch gap. Gapping is not optional: boards need room to shed water and to move with humidity, and a tight-butted deck cups and traps debris. On waste, a straight layout carries about 8 percent for end cuts and the odd defect; a diagonal (45 degree) layout jumps to about 15 percent because every board hits the rim at an angle and the cut-offs are longer. These are standard estimating conventions, not hard rules; on a complex deck with lots of picture-frame borders, budget more.
Board feet, linear feet, and square feet
Three units show up on a deck order and they are not interchangeable. Square feet is the deck surface (length x width) and drives screw count. Linear feet is how decking is actually sold and priced, which is why this tool reports both a board count and total LF. Board feet is the volume unit for framing lumber (the joists, beams, and posts under the deck): board feet = thickness x width x length in feet, divided by 12. Use the board foot calculator for the substructure lumber and this tool for the surface.
From board counts to a priced bid
Deck boards and screws are one page of a deck estimate. The joists, beams, posts, footings, ledger, flashing, and hardware all come off the plan, and pricing the whole assembly against your own cost book is where the bid is won or lost. Ruh reads the plan set, counts the full framing and decking package, and drafts a priced estimate you can stand behind. See how it works on the framing estimating software page.
Decking calculator FAQs
How many deck boards do I need?+
Count rows across the deck width, then multiply by the deck length. Each 5.5 inch board plus a 1/4 inch gap covers 5.75 inches, so a 12 ft wide deck needs ceil(144 / 5.75) = 26 rows. On a 16 ft deck that is 26 x 16 = 416 linear feet, about 449 LF with 8 percent waste, or 29 boards at 16 ft each.
What joist spacing do I need for composite decking?+
12 inches on-center for composite boards run perpendicular to the joists, versus 16 inches on-center for wood. Composite is less stiff and sags at wider spacing, so most manufacturers require the tighter layout (8 to 10 inches for a diagonal pattern). Check the board's span table, because the warranty depends on it.
How many screws per square foot of decking?+
About 3.5 screws per square foot with hidden or face fasteners on 16 inch joists. A 192 square foot deck needs roughly 192 x 3.5 = 672 screws. Tighter joist spacing or double-screwing at the ends pushes that number up.
How much gap should I leave between deck boards?+
About 1/4 inch. Boards need room to drain water and to expand and contract with humidity. This calculator builds the gap into the row math (5.5 inch face + 1/4 inch gap = 5.75 inches per row), so the board count already accounts for it.
Straight or diagonal decking, and how much does it change waste?+
A straight layout carries about 8 percent waste; a diagonal (45 degree) layout runs about 15 percent because every board meets the rim at an angle and the cut-offs are longer. On a 449 LF straight deck, switching to diagonal adds roughly 30 LF of board.
Ruh counts the whole deck package, not one board.
AI takeoff reads your plan set, counts decking, joists, beams, posts, and hardware, and drafts a priced estimate on your own cost book.
More tools: board foot calculator and stud calculator
Figures on this page are illustrative. Construction estimates depend on project-specific conditions, source documents, market pricing, and professional judgment. Ruh's AI assists the estimator and does not replace professional review: your team reviews, validates, and approves every estimate, bid, and pricing decision.