Deck flooring calculator

Lay deck boards across a width with a stated gap and count stock lengths along the deck.

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Deck width

Deck length along boards

More inputs and assumptions

Actual board face width

Gap between boards

Stock board length

Answer

…

Lay deck boards across a width with a stated gap and count stock lengths along the deck.

More results

Precision and calculation record

Decimal places in numeric results and text downloads

Rounding changes displayed numbers, not the calculation. Text, fractions, matrices and CSV schedules keep their own formatting. Automatic keeps up to 12 significant digits, with money shown to cents where applicable.

Saved scenario

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Formula and assumptions

Board count = ceiling((deck width + gap)/(board width + gap)). No outer-edge gap is added. Assumes straight parallel boards, no offcut reuse and no allowance. Joists, fastening, expansion and structural design are outside this quantity model. If the last edge lands inside a gap, change width, gap or board width; a zero-width final board is rejected.

Automatic precision shows numbers to 12 significant digits. Thousands separators such as 1,000 are accepted; use a dot for decimals.

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Updated 2026-09-26

Using Deck flooring calculator

Lay deck boards across a width with a stated gap and count stock lengths along the deck.

Next: Board foot calculator

A worked example

Example inputs: deck width = 2.99, deck length along boards = 4, actual board face width = 0.14, gap between boards = 0.01, stock board length = 4. Deck boards across the width = 20.

Before you use the result

Example results for deck width

These examples use Deck length along boards: 4; Actual board face width: 0.14; Gap between boards: 0.01; Stock board length: 4. They are reference calculations, not recommended settings.

Deck width	Deck boards across the width
2.99	20
5.98	40

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ToolOctopus. “Deck flooring calculator.” Updated 2026-09-26. https://tooloctopus.com/deck-flooring-calculator.

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