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Deck Calculator

Enter the deck size and the boards you're using. We count the rows across the deck, convert them to stock-length boards, and estimate the screws at two per board/joist crossing.

Diagram of deck boards laid side by side across a deck, with the deck length and width marked
Deck boards run side by side with a small gap; board length spans the deck's width.

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Enter your measurements

How deck boards and screws are calculated

Boards: each row of decking covers the board's actual width plus the drainage gap. A nominal 2×6 or 5/4×6 board is 5.5 in wide in reality; with a 1/4 in gap each row covers 5.75 in. Rows = deck width ÷ coverage, rounded up. Partial rows count as a full board. Rows × the deck length gives total linear feet, and boards to buy = rows × ⌈deck length ÷ stock length⌉.

Screws: two at every board/joist crossing. Crossings per row = the number of joists the board passes over (deck length ÷ joist spacing, + 1). At 16 in joist spacing a 16 ft board crosses 13 joists, so 26 screws per board. Hidden fastener systems use clips at the same crossings, so the count holds for those too.

The board count then adds your waste allowance on top of the installed rows, for cuts, splits and the odd warped board. Screws are counted on the installed layout; a 10% board allowance leaves you spare boards, not spare screws, so grab one extra box if you're near a round number.

Not counted here: the frame itself (joists, beams, posts, ledger), stairs, and railing. And if your deck is wider than your stock length in the board direction, stagger the butt joints and add a few percent for cuts. Posts need concrete footings. Size them with the Post Hole Concrete Calculator.

Worked examples

16 × 12 ft deck, 5.5 in boards

1/4 in gap, joists 16 in o.c., 16 ft stock: 26 rows installed, 13 crossings per board, +10% waste on boards.

Buy 29 boards + ≈ 676 screws

10 × 10 ft deck, 3.5 in boards

2×4 decking, 1/4 in gap, 10 ft stock: 32 rows installed, +10% waste.

Buy 36 boards + ≈ 512 screws

20 × 14 ft deck, 5.5 in boards

3/16 in gap; 30 rows × 2 boards per row at 16 ft stock, +10% waste.

Buy 66 boards + ≈ 960 screws

Frequently asked questions

How many deck boards do I need for a 12×16 deck?
With 5.5 in boards and a 1/4 in gap: 26 rows, and one 16 ft board per row: 26 boards installed, or 29 to buy with a 10% waste allowance. That's about 416 linear ft of decking, and roughly 676 screws at 16 in joist spacing.
What gap should I leave between deck boards?
1/4 in is the common drainage gap for dry lumber; 1/8–3/16 in for pressure-treated boards that will shrink as they dry, and for many composite systems. The gap is part of each row's coverage in this calculator, so it directly changes the count.
How many screws are in a pound / box?
A 1 lb box of 2.5 in deck screws holds roughly 55–60 screws; a 5 lb box about 280–300. This calculator gives the screw count. Divide by ~56 for pounds to buy, and round up: running out mid-row is miserable.
Should boards run along the length or the width?
Whichever you enter as 'length'. The calculator assumes boards run that way. Running boards along the longer dimension usually means fewer butt joints. Diagonal layouts use more material on cuts. Pick the 15% waste setting for those.
Does this include the deck frame and footings?
No. It's the decking layer only. Joists are usually the same lumber family (2×8 or 2×10 at the spacing you chose), and footings can be sized with the Post Hole Concrete Calculator once you know the post layout.

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Estimate disclaimer: results are planning estimates based on standard manufacturer yields and coverage figures. Site conditions, product choice and installation method change actual quantities. Verify before you buy, and follow local building code for structural work. This tool does not replace professional engineering advice.

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