Deck Board Calculator
Accurately estimating the number of deck boards requires accounting for board width, the gap between boards, and a waste allowance for cuts and defects. This calculator takes your deck's length and width, the nominal board width, and the desired gap to compute exactly how many boards you need — and how many linear feet of lumber to purchase.
An optional joist estimator helps you plan the structural framing: enter your preferred joist spacing (typically 16 inches on center) and the tool will tell you how many joists span the deck width and the total linear feet required. Both imperial (feet/inches) and metric (meters/centimeters) unit systems are supported.
How it works
Board count (before waste) = ⌈deck_length ÷ (board_width + gap)⌉. Total boards = ⌈board_count_raw × (1 + waste% ÷ 100)⌉. Linear feet = total_boards × deck_width. For joists: joist_count = ⌊deck_width ÷ joist_spacing⌋ + 1; total joist linear feet = joist_count × deck_length.
Use cases
- Estimating lumber costs for a new backyard deck build
- Planning material quantities before visiting a lumber yard
- Calculating board requirements for composite or PVC decking
- Determining joist framing needs for deck structural planning
- Comparing board widths to minimize offcuts and waste