Deck Calculator

Use Deck Calculator

Figures update as you type. Nothing you enter leaves this tab, and no values are stored.

Deck length (ft)Deck width (ft)Board width (in)

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About Deck Calculator

A deck calculator estimates the area of a deck and how many rows of boards it takes to cover, from the deck's dimensions and the width of your decking boards. Decking is bought by length and laid in rows, so the count that matters is how many rows of your chosen board width span the deck - plus an allowance for the small gaps between boards and the offcuts at the ends. The tool works out the deck area and divides the width by your board width to get the number of rows. Standard boards are about 5½ inches wide; composite and hardwood vary, so enter the real figure. Plan gaps, borders and cutting waste separately; this calculation does not incorporate their dimensions. Joists and framing are a separate calculation from the surface boards counted here.

Using Deck Calculator

Measure the length along the direction the boards will run and the width across the board rows. Enter both in feet; switching them changes the row count even when the area stays the same.
Measure the actual board width in inches rather than using its nominal product name. The calculation divides the deck width by that board width and rounds up to a whole row.
Use the row count to plan board lengths and end joints. A row may require more than one purchased board. Make a cutting list using the available stock lengths before ordering.

Where deck calculator helps

Decking a patio

A 16×12 ft deck is 192 ft²; with 5½-inch boards that is about 27 rows before waste.

Before you use the result

This model does not subtract drainage gaps from the row calculation or add a border. Follow the selected decking system's gap and support instructions, then adjust the layout and cutting list accordingly.
A 16 by 12 ft rectangle with 5.5-inch boards has 27 calculated rows. If boards only come in 8 ft lengths, that does not mean buying 27 boards: each 16 ft row needs at least two pieces before considering joint support and offcuts.
Joist spacing, foundations, fasteners, railing and structural loads are outside this surface-area estimate. A waste percentage cannot replace a design for those parts. Keep the board layout and material calculation separate from structural approval.

Questions about Deck Calculator

How many deck boards do I need?

The result counts rows across the deck, not purchased stock boards. Multiply each row by its required length, then plan joints and cuts against available board lengths. Gaps and borders need separate layout checks.

Is my data saved or uploaded?

No. Deck Calculator calculates the result entirely in this browser; the values you enter are not stored or sent to a server.