Deck Square Footage Calculator
Calculate deck surface area for decking boards. Includes adjustments for board widths and a 10% waste factor for cuts and edge boards.
Deck Calculator
Decking board math
Most decking boards are 5.5 inches wide (nominal 6 inch) with a 1/4 inch gap. So each linear foot of board covers about 0.48 sq ft of deck. A 200 sq ft deck needs roughly 416 linear feet of boards, divided by your board length.
For a 12 ft long deck using 12 ft boards, the math is easy. For deck dimensions that aren't board-length friendly, you'll have butt joints — and those add 5–10% waste.
Composite vs. wood
Composite decking is sold by the linear foot — calculate exact lengths needed plus 10%. Pressure-treated wood is sold by the board, so you may have to round up to standard 8/10/12/16 ft lengths.
Don't forget framing: joists, beams, and ledger boards aren't in your decking sq ft, but they're a major cost. Get a separate framing estimate.
Deck board math beyond simple square footage
Deck boards are typically 5.5 inches wide (after the standard 1/4-inch gap between boards) and come in lengths from 8 to 20 feet. To calculate boards needed, divide deck width by board width:
12 ft wide deck with 5.5-inch boards: 12 × 12 ÷ 5.5 = 26.2 board widths needed. Round up to 27 boards.
Deck length determines board length: ideally one continuous board per row. 16 ft long deck = order 16-ft boards. 20 ft deck = order 20-ft boards or accept butt joints.
Total board feet for 12 × 16 deck: 27 boards × 16 ft = 432 linear feet of decking. At 5.5-inch board width that's 432 × (5.5/12) = 198 sq ft of board surface (close to the 192 sq ft of deck area, accounting for the small gap).
Composite decking is sold by the linear foot, hardwood and pressure-treated by the board (length × width × thickness specified). Always specify both linear feet AND square footage when ordering — vendors quote both depending on the product.
Joists, posts, and the framing below
Deck building involves substantially more lumber than just the visible boards. The framing under the deck consumes 50-70% of the total lumber budget.
Joists: typically 2×8 or 2×10 boards spaced 16 inches on center. For a 12 ft wide deck: 12 × 12 / 16 = 9 joists needed. Each joist is the length of the deck (16 ft for a 12×16 deck). Total: 9 × 16 = 144 linear feet of joist material.
Beams: typically doubled 2×10s or 2×12s. For a 12 ft deck: usually 2 beams running the 12 ft direction, each made of two 12 ft boards = 4 boards × 12 ft = 48 linear feet of beam material.
Posts: 4×4 or 6×6 verticals from concrete footings to beams. Typically 4 corner posts + 1 mid-run post per 6-8 ft of beam length. A 12 × 16 deck needs 6-8 posts.
Joist hangers, post brackets, lag bolts, deck screws: $200-500 in fasteners for a typical deck.
Decking material cost per sq ft (installed)
Total deck cost varies enormously by material choice. Per-square-foot fully installed (2024 prices):
Pressure-treated pine: $20-40 per sq ft installed. Standard 15-20 year lifespan with regular staining.
Cedar: $30-50 per sq ft installed. Naturally rot-resistant; 20-30 year lifespan.
Composite (Trex, TimberTech, Fiberon): $35-70 per sq ft installed. 25-50 year warranty. Most popular mid-range option.
PVC (Azek, Wolf): $40-80 per sq ft installed. Doesn't fade as much as composite; lighter colors stay cooler.
Tropical hardwoods (Ipe, Cumaru, Tigerwood): $50-100+ per sq ft installed. 50-75 year lifespan. Premium aesthetic.
For a 12 × 16 ft deck (192 sq ft): pressure-treated $3,800-7,700, composite $6,700-13,400, ipe $9,600-19,200.
Pro tips
Use longer boards
Longer boards mean fewer butt joints. Try to size your deck to standard board lengths.
Add 10% for waste
Cuts at corners and miters waste material. Plan for 10% extra.
Don't forget fascia
Fascia and skirt boards are sold separately and often forgotten. Measure perimeter × board height.
Stairs need extra
Treads and risers add up. Calculate stair area separately and add it to your deck total.