About the deck board calculator
Deck boards are labeled by nominal size, but their actual width is smaller — a nominal 6-inch board is usually about 5.5 inches wide. This calculator uses the actual width plus the gap between boards to count rows, then converts the total length into the board length you’ll buy.
How to use this calculator
- Enter the deck length (the direction boards run) and width.
- Enter the actual board width and gap.
- Enter the board length you’ll purchase.
- Choose a waste allowance.
Worked examples
- Board 5.5 in + gap 3/16 in = 5.69 in per row
- Rows: 12 ft ÷ 0.474 ft = 25.3 → 26
- Linear: 26 × 16 × 1.10 = 457.6 ft
- 16 ft boards: 457.6 ÷ 16 = 28.6
29 boards.
Measurement guidance
Board gaps
Gap requirements differ between wood and composite decking. Use the manufacturer’s recommended spacing.
Board length
Choosing boards that match the deck length avoids butt joints and reduces waste.
Frequently asked questions
Why use actual width?
Nominal sizes are larger than real dimensions. Using nominal width would undercount the boards.
How much waste should I add?
Around 10% covers end cuts and rejected boards for simple decks.
Does this include stairs?
No. Calculate stair treads separately.