The Formula Behind This Calculator
Coverage per board = board face width + gap (inches)
Boards = round up (deck width in inches / coverage per board)
Joists = floor (deck length in inches / joist spacing) + 1, each as long as the deck width
Screws = boards x joists x 2, boards to buy = round up (boards x 1.10)
Decking is a covering problem in one direction: the boards run the length of the deck, so the count is set entirely by the width and by the strip each board covers, which is its face width plus one gap. The gap matters more than people expect. A quarter inch gap on a 5.5 inch board means about 4 percent of your width is air, and ignoring it undercounts a wide deck by a full board. Joists run the other way, spaced along the length, with one at each end, which is why the joist formula adds one. Screws follow the grid: wherever a board crosses a joist, it gets two screws, so the fastener count is just the size of that grid times two.
Worked Example: A 16 by 12 Ground Level Deck
A simple rectangular deck is 16 feet long by 12 feet wide, decked with standard 5.5 inch boards, a 1/4 inch gap, and joists 16 inches on center.
- Coverage per board: 5.5 + 0.25 = 5.75 inches.
- Boards: 144 inches of width / 5.75 = 25.04, round up to 26 boards, each 16 feet long.
- Total decking: 26 x 16 = 416 linear feet. With 10 percent waste, buy 29 boards.
- Joists: 192 inches / 16 = 12 spaces, plus 1 = 13 joists, each 12 feet long.
- Screws: 26 boards x 13 joists x 2 = 676 screws, about 5 pounds.
- Budget: the 29 boards you buy are 464 linear feet, and at $1.20 to $1.90 per linear foot for pressure treated decking that is about $557 to $882, October 2026 national retail pricing.
Switch the joist spacing to 12 inches in the tool and watch the joist count climb to 17 and the screw count with it. That stiffer frame is the right call for a diagonal layout, and seeing the fastener and lumber difference up front is exactly how you decide whether the diagonal look is worth its premium.
A Complete Guide to Estimating Deck Materials
A deck surface is one of the most satisfying weekend builds, and also one where the materials list has three separate systems hiding inside it: the decking itself, the joist grid under it, and the fasteners that tie them together. Estimate any one of them by eye and you will be short. This guide walks through each system, the gaps and spacing choices that change the numbers, and what a realistic budget looks like.
Board Width, Gap and the Shrinkage Question
The width printed on a deck board is its actual face width for most products: 5.5 inches for the standard board, whether it is a 2x6 or a 5/4 board. Pressure treated lumber is sold wet and shrinks as it dries, so boards installed tight together can open up to a 3/8 inch gap by the end of the first summer. Experienced builders install wet treated boards with a small 1/8 inch gap and let shrinkage set the final spacing, while kiln dried lumber and composite boards, which barely move, are set at their final gap of about 1/4 inch. Enter the gap you will actually install at, since it changes the board count on wide decks. Whatever you choose, keep the gap consistent: drainage and drying depend on it, and a deck with random spacing looks homemade even when the structure is perfect.
The Joist Grid Under the Surface
Joists do not show, but they decide whether a deck feels solid or trampolines underfoot. Sixteen inches on center suits wood decking and most composites laid straight. Diagonal decking effectively lengthens the span each board crosses, so it needs 12 inch spacing, and many composite makers require 12 inches for their thinner boards and for stair treads. The joist count in this calculator assumes joists run across the width and repeat along the length, with one at each end. Add blocking or a picture frame border to your lumber list if your design has them, and remember the rim joist that caps the ends: one board the length of the deck on each long side. None of that framing includes beams, posts or concrete footings, which are sized from span tables and local frost depth rather than counted, and your building department will want to see those numbers on a permit drawing.
What a Deck Surface Costs in 2026
Materials as of October 2026, based on national retail pricing: pressure treated deck boards run about $1.20 to $1.90 per linear foot depending on length and grade, cedar about $2 to $3, and composite boards about $2.50 to $4.50 per linear foot, with capped composite at the top of that range. Joist lumber, hangers and hardware for a deck this size typically add $300 to $600, and a 5 pound box of quality deck screws runs $35 to $55. Fully hired out, published cost surveys put a new wood deck around $30 to $45 per square foot and composite around $45 to $65, which for a 192 square foot deck is roughly $5,800 to $12,500. The DIY surface only path, on an existing sound frame, is the budget outlier at roughly $800 to $2,000 in materials.
Ordering and Building Habits
- Sight down every board at the store and reject the bowed and twisted ones. Lumber yards expect it on decking.
- Buy boards in the full deck length when possible. Butt joints mid span waste material and telegraph through the surface.
- Pre drill the ends of wood boards near edges to stop splits, and set screws a consistent inch from each edge.
- Seal the cut ends of pressure treated boards with end cut preservative. The treatment does not reach the core of a cut.
- Store the 10 percent leftover boards flat, covered and off the ground for future repairs, since new boards weather to a different color than aged ones.