Deck Boards, Joists & Footings Estimator
A free deck material calculator for the whole build: decking boards by stock length, joists and beams, concrete footings in bags, and deck screws, with a waste allowance built in.
How to Estimate Deck Materials
A deck material list breaks into four parts: the decking boards on top, the joists and beams that frame it, the concrete footings that hold it up, and the screws that tie it together. Enter the deck length and width, pick your decking and framing, and the calculator above returns board counts, joist and beam counts, footing concrete in bags and cubic yards, and screw pounds, with a waste allowance built in. The length is the direction the joists span.
Decking Boards per Square Foot
Board coverage depends on the face width and the gap between boards. Divide 12 by the width plus the gap to get linear feet per square foot. A 5/4x6 or 2x6 board is 5.5 inches wide, so at a 1/8 inch gap it lays about 2.13 linear feet per square foot. A narrower 5/4x4 at 3.5 inches takes about 3.31 linear feet per square foot, which means more boards and more screws.
| Decking Board | Face Width | Linear Ft per Sq Ft (1/8 in gap) |
|---|---|---|
| 5/4 x 6 (standard deck board) | 5.5 in | 2.13 |
| 2 x 6 | 5.5 in | 2.13 |
| 5/4 x 4 | 3.5 in | 3.31 |
Joists, Beams, and Post Spacing
Joists run the short way and carry the decking. Frame them at 16 inches on center for most boards, 12 inches for a diagonal pattern or heavier load, and 24 inches only where a composite board is rated for it. The joist count is the deck width in inches divided by the spacing, plus one for the starting joist. Deeper joists span farther: a 2x8 covers less distance between beams than a 2x10 or 2x12.
The beam catches the joist ends and passes the load to the posts and footings. A deck attached to the house with a ledger needs one beam at the outer edge; a freestanding deck needs a beam on each side. Doubling or tripling the beam ply lets the posts sit farther apart. Always confirm joist and beam spans against your local code span tables before you build.
Footings and Concrete
Each post sits on a concrete footing dug below the frost line, often 36 to 48 inches deep. Space footings by what the beam can carry between posts, usually 6 to 8 feet. A round footing holds pi times the radius squared times the depth: a 12 inch diameter hole 36 inches deep is about 2.36 cubic feet, or 4 bags of 80 pound mix. Order the total by the bag, or by the cubic yard for larger jobs with the concrete calculator.
What a Deck Costs
Materials for a pressure treated deck usually run about $15 to $25 per square foot, while composite decking runs about $30 to $60 per square foot for materials alone. Installed by a contractor, a deck typically runs $40 to $90 per square foot depending on the decking you choose, the height off the ground, and whether the job includes stairs and railing.
Stairs and railing are priced separately from the deck field. Use the board, framing, footing, and screw counts above to price the structure, then add your stair and rail materials on top.
Deck Building FAQ
Divide 12 by the board face width plus the gap to get linear feet per square foot, multiply by your deck area, add waste, then divide by the stock board length. A 5/4x6 board is 5.5 inches wide at a 1/8 inch gap, which is about 2.13 linear feet per square foot, so a 320 square foot deck needs roughly 750 linear feet, or about 47 boards of 16 foot stock at 10 percent waste.
Most decks frame joists at 16 inches on center; 12 inches is used for diagonal decking or heavy loads, and 24 inches only for some composite systems that allow it. Count is the deck width in inches divided by the spacing, plus one for the starting joist. A 20 foot wide deck at 16 inches on center needs 16 joists.
Footings sit under the beam, spaced by the beam span the posts can carry, commonly 6 to 8 feet. Divide the beam length by that spacing and add one. A 20 foot beam at 8 foot spacing needs 4 footings. A freestanding deck has a beam on each side, so it needs footings under both.
A round footing holds pi times the radius squared times the depth. A 12 inch diameter footing 36 inches deep is about 2.36 cubic feet, which is 4 bags of 80 pound concrete mix. Four of those footings need about 9.4 cubic feet, or 16 bags.
Materials for a pressure treated deck usually run about $15 to $25 per square foot, and composite decking runs about $30 to $60 per square foot for materials. Installed by a contractor, expect roughly $40 to $90 per square foot depending on decking, height, stairs, and railing.
A deck attached to the house with a ledger uses a joist hanger at every joist where it meets the ledger, so the count matches the joist count. A freestanding deck that rests on beams on both sides does not need hangers at the ends, though you still flash and fasten properly.