Estimate how many deck boards to buy, plus total linear footage and deck area, from your deck's dimensions, board width and length, gap spacing, and a waste allowance.
Results
Calculated
Boards to Buy
—
Full-length boards, waste included
Total Linear Feet
—
Decking length needed, waste included
Deck Area
—
Length × width
Rows Across Width
—
Boards laid edge to edge across the width
Add this calculator to your website
How to use this calculator
Enter your deck's length and width, the actual width and stock length of the boards you plan to use, the gap you'll leave between boards, and a waste allowance for cuts and mistakes. Click Calculate to see how many boards to buy, the total linear footage needed, the deck area, and the number of board rows across the width.
The formula
Deck boards are laid in rows across the width of the deck, each row running the full length. The number of rows equals the deck width divided by one board's actual width plus the gap, rounded up — a partial row still needs a full board:
Rows = ceil(deck width ÷ (board width + gap))
Each row uses one deck-length's worth of board, so total linear feet of decking is rows × deck length, then increased by your waste percentage to cover trimming, staggered seams, and mistakes. Dividing that by the stock board length and rounding up gives the number of boards to purchase:
Lumber is sold by nominal size, but the actual milled size is smaller. A nominal 2×6 deck board is actually about 5.5 inches wide, a 2×4 is about 3.5 inches, and a 2×8 is about 7.25 inches. Always enter the actual width — using the nominal size will undercount how many rows you need.
Frequently Asked Questions
How many deck boards do I need?
Divide the deck width by one board's actual width plus the gap to get the number of rows (rounded up), multiply by the deck length for total linear feet, add your waste allowance, then divide by the board's stock length and round up. This calculator performs that calculation automatically from your inputs.
What size gap should I leave between deck boards?
Most builders leave 1/8 to 3/16 inch (0.125 to 0.1875 in) between boards for drainage and to let wood expand when wet. Composite decking often specifies its own gap in the manufacturer's instructions, so check those first if you are not using wood.
Why add a waste allowance?
A waste allowance covers boards lost to squaring off ends, cutting around posts or stairs, culling warped or damaged pieces, and staggering seams between rows so joints do not line up. Ten percent is a common starting point for a simple rectangular deck; layouts with many cuts may need fifteen percent or more.
Should I enter nominal or actual board width?
Enter the actual milled width, not the nominal lumber size. A nominal 2x6 board is actually 5.5 inches wide, a 2x4 is 3.5 inches, and a 2x8 is 7.25 inches. Composite and PVC boards list their actual width directly on the product spec sheet.