Deck Board Calculator — boards and linear feet

How it works

To board a deck, divide the deck area by the area one board covers, adding a waste allowance for cuts and offcuts:

boards = ⌈area × (1 + waste) ÷ board coverage⌉

A board's coverage is its width in inches ÷ 12 (to get feet) times its length in feet. A 5.5-inch-wide, 12-foot board covers (5.5 ÷ 12) × 12 = 5.5 square feet. The calculator also reports the total linear feet (boards × length), which is how decking is often priced.

A 10% waste allowance covers cut ends, offcuts and the occasional defect. This is a board count — it does not subtract for the small gaps left between boards for drainage, which slightly increase the real coverage, so counting by area with a waste margin stays on the safe side.

Worked example

A 200 sq ft deck with 5.5 in × 12 ft boards (5.5 sq ft each) and 10% waste needs (200 × 1.1) ÷ 5.5 = 40 boards, or 480 linear feet. Using wider 7.25 in boards drops it to 31 boards. A smaller 120 sq ft deck with 8 ft boards takes 36 boards (288 linear feet).

Frequently asked questions

How many deck boards do I need?

Divide the deck area (plus waste) by the area one board covers and round up. A board's coverage is its width in inches ÷ 12 times its length in feet. For 200 sq ft of 5.5 in × 12 ft boards with 10% waste, that is 40 boards.

What is the difference between board count and linear feet?

Board count is how many physical boards to buy; linear feet is the total length of all those boards (count × length), which is how decking is often sold and priced. This calculator gives both. Multiply linear feet by the price per foot for a cost estimate.

How much waste should I allow for decking?

About 10% for a simple rectangular deck, covering cut ends and offcuts. Angled, picture-frame or diagonal patterns waste more — allow 15%. Longer boards that span the deck in one piece waste less than short boards with many joints.

Do I need to account for gaps between boards?

Gaps (about 1/8 inch) for drainage and expansion slightly increase the area each board effectively covers, so counting by area without subtracting gaps is a small over-estimate — which, with the waste allowance, keeps you from running short. For a tight estimate, add the gap to the board width.

What board width should I use?

Nominal "5/4 × 6" decking is about 5.5 inches wide actual; 2×6 is also 5.5 inches, and some boards are 3.5 (2×4) or wider. Composite boards vary. Use the actual width of the board you are buying for the count to come out right.

Does this include the framing or fasteners?

No — it counts the surface decking boards only. Joists, beams and posts are framing (calculated from the deck plan and span), and screws or hidden clips are estimated from the board count. Work those out separately.