Waste factor, batches and storage
Even a careful board count is not the same as an order quantity. Waste, colour matching and delivery units change what you should buy.
Simple rectangles may need about 5–10% extra. Complex shapes often need more. Composite colour batches make short re-orders harder.
Order enough in one go when colour consistency matters.
Keep boards flat, supported and protected until install.
Estimate boards, joists and materials from deck size, board width and spacing.