How many deck boards do I need?
Estimate deck boards from deck size, board width, board length, and a realistic trimming waste buffer.
A deck board estimate starts with deck area, but the number you actually buy depends on board width, board length, layout, trimming, and waste.
1. Measure deck length and width
For a simple rectangle, multiply length by width to get square footage. For an L-shaped deck, split it into rectangles and add the areas.
2. Use actual board width
Nominal lumber sizes are not the same as actual sizes. A common 5/4 deck board is often about 5.5 inches wide. Use the actual width listed by the store or manufacturer.
3. Pick the board length you plan to buy
Common lengths include 8, 10, 12, 16, and 20 feet. Longer boards can mean fewer butt joints, but they may cost more and be harder to transport.
4. Add waste
Ten percent is a practical start for a rectangular deck. Add more for picture-frame borders, diagonal patterns, stairs, angled cuts, or boards with defects.
Quick formula
deck area / board width in feet x waste buffer / board length = boards to buy