How Many Deck Boards Do I Need? 2026 Calculator and Formula

The deck board question looks simple and trips people up anyway, because the number on the label (6 inches) is not the coverage you get (5.5 inches plus a gap). This guide gives you the exact formula contractors use, a coverage table for every common board size, and worked examples for the most common deck sizes in 2026.

The Deck Board Formula

Rows = deck width / (actual board width + 1/8 in gap). Boards = rows x (deck length / board length, rounded up) x (1 + waste %).

A nominal 6-inch board (5/4x6 or 1x6) actually covers 5.5 inches, and you add a 1/8-inch gap between boards for drainage — so each row covers 5.625 inches, or 0.469 ft. For a 12-ft-wide deck that is 12 / 0.469 = 26 rows. If the deck is 16 ft long and you buy 16-ft boards, that is one board per row: 26 boards, plus 10% waste = 29 boards.

Board Coverage by Size

• 1x4 / 5/4x4 (3.5 in actual): covers 0.302 ft per row — about 2.15 sq ft per 8-ft board
• 1x6 / 5/4x6 (5.5 in actual): covers 0.469 ft per row — about 5.5 sq ft per 12-ft board
• 2x6 (5.5 in actual): same coverage as 5/4x6, heavier and stiffer
• 2x8 (7.25 in actual): covers 0.615 ft per row — about 7.4 sq ft per 12-ft board
• 2x10 (9.25 in actual): covers 0.781 ft per row — about 9.4 sq ft per 12-ft board

Board Counts for Common Deck Sizes (5/4x6, 10% Waste)

• 10x10 (100 sq ft): 22 rows x 1 board = 24 boards (10 ft)
• 12x12 (144 sq ft): 26 rows x 1 board = 29 boards (12 ft)
• 12x16 (192 sq ft): 26 rows x 1 board = 29 boards (16 ft)
• 16x16 (256 sq ft): 35 rows x 1 board = 39 boards (16 ft)
• 16x20 (320 sq ft): 35 rows x 1 board = 39 boards (20 ft), or 78 boards at 10 ft
• 20x20 (400 sq ft): 43 rows x 1 board = 48 boards (20 ft)

How Much Waste Allowance Do You Need?

Straight layouts with boards running the full deck length need 10% waste — that covers end cuts, the occasional split or warped board, and one or two boards you will want to replace in year three. Diagonal (45-degree) layouts need 15% because every board ends in an angled cut. Herringbone and picture-frame borders can push waste to 20%.

2026 Board Prices per Linear Foot

• Pressure-treated 5/4x6: $1.10–$1.60/lf ($13–$19 per 12-ft board)
• Cedar 5/4x6: $2.20–$3.40/lf ($26–$41 per 12-ft board)
• Composite 1x6: $2.60–$3.80/lf ($31–$46 per 12-ft board)
• Capped PVC 1x6: $4.20–$6.00/lf ($50–$72 per 12-ft board)

Frequently Asked Questions

Should I run boards along the length or the width?

Run them perpendicular to the joists, and buy board lengths that span the full deck in one piece whenever possible. A 16-ft deck with 16-ft boards has zero butt joints; the same deck with 8-ft boards has a seam on every row, more cuts, and more waste.

How many screws do I need per board?

Two screws at every joist crossing. A 12-ft board on a 12-ft-wide deck with joists at 16 in on center crosses about 10 joists, so 20 screws per board. A 300 sq ft deck typically uses 1,200–1,500 screws — about 6 one-pound boxes.

Can I mix board lengths to save money?

Yes, if you plan the seam pattern first. Stagger butt joints so no two adjacent rows break on the same joist, and land every seam on a joist with both board ends screwed down. Random mixing without a plan is how decks end up with two-inch slivers at the house wall.