How deck boards are counted
Deck boards usually run parallel to the house and cross the joists. The number of rows depends on the deck width and the board width plus the gap. Each row is as long as the deck, so rows times length gives the linear feet of decking.
Rows = deck width (in) ÷ (board width + gap), rounded up
Boards = rows × deck length × (1 + waste) ÷ board length, rounded up
Worked example
A 16 by 12 foot deck with 6 inch boards and a 3/16 inch gap: 144 ÷ 5 11/16 = 25.3, so 26 rows. 26 rows × 16 feet = 416 linear feet, or 458 with 10% waste. In 16 foot boards that is 29 boards. Joists at 16 inches on center across 16 feet need 13 joists, each 12 feet long.
Good to know
- The joist count here is the field joists plus both end joists. Add rim joists, ledger and beams separately.
- Buy board lengths that match the deck length so you avoid butt joints. A 16 foot deck with 16 foot boards has none.
- Use 15% waste for diagonal or picture-frame layouts.