Deck Calculator

Estimate decking boards, board rows, pieces per row, joist lines, fasteners and material cost for a rectangular deck. Enter the actual product dimensions and spacing.

Unit system

Board direction

Joists are estimated perpendicular to the boards.

Deck length (ft)

Deck width (ft)

Actual board face width (in)

Gap between boards (in)

Available board length (ft)

Joist spacing (in, on center)

An editable spacing input, not a structural recommendation.

Fasteners per board/joist crossing

Material allowance (%)

Optional prices

Use one currency. The calculator does not supply market prices.

Price per full decking board

Joist material price per ft

Price per fastener

Deck material formulas

Let the board-direction span be the deck dimension parallel to the boards and the cross dimension be perpendicular to them.

Board rows = ceiling[(cross dimension + gap) ÷ (board width + gap)]. Adding one gap to the numerator avoids counting an imaginary gap after the last row.

Pieces per row = ceiling(board-direction span ÷ available board length).

Full boards before allowance = rows × pieces per row. Boards to order = ceiling(full boards × (1 + allowance % ÷ 100)).

Joist lines = ceiling(board-direction span ÷ entered joist spacing) + 1. Estimated joist length = joist lines × cross dimension.

Fasteners = board rows × joist lines × fasteners per crossing, rounded upward after the allowance.

Scope: this is a rectangular material estimator. It does not select joist size or span, beams, posts, footings, ledgers, hangers, blocking, rim boards, railing, stairs or connections. It does not optimize staggered joints or reuse offcuts. Diagonal, curved, picture-frame and multi-level layouts require a separate cutting plan and may use more material. Confirm structural design and locally required permits before construction.

Six calculated examples

Inputs	Estimated result
16 × 12 ft deck; boards along 16 ft; 5.5 in boards, 1/8 in gap, 16 ft stock, 10% allowance	192 ft²; 26 rows; 29 boards to order
Same deck with 8 ft stock boards	2 pieces per row; 52 boards before allowance; 58 to order
16 × 12 ft deck; boards along the 12 ft width; 16 ft stock	35 rows; 39 boards to order
12 × 12 ft deck; 5.5 in boards, 1/8 in gap, 12 ft stock, no allowance	144 ft²; 26 rows; 26 boards
5 × 4 m deck; boards along 5 m; 140 mm boards, 5 mm gap, 5 m stock, 10% allowance	20 m²; 28 rows; 31 boards to order
4 × 3 m deck; boards along 4 m; 90 mm boards, 5 mm gap, 2 m stock, 5% allowance	32 rows; 2 pieces per row; 68 boards to order

How to use this deck calculator

Measure the rectangular deck length and width and choose the direction the decking boards will run.
Enter actual board face width and the planned gap, not only the nominal lumber name.
Enter a board length you can purchase. The estimate counts whole pieces and does not assume that offcuts can be reused.
Enter the joist spacing supplied by the approved design and the fastening pattern required by the product.
Choose an explicit allowance. Prices are optional and should come from the same supplier and currency.

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Deck Calculator: Boards, Joists, Fasteners and Cost