Deck Board Calculator: How Many Boards, Screws and Clips?

Quick answer: a 12 x 16 ft deck with boards running the 16 ft way, using 5-1/2" wide boards and a 3/16" gap, needs 26 rows of boards. That is 29 boards of 16 ft with 10% extra, plus about 680 screws (2 per board at every joist, joists at 16").

Deck board calculator

Deck length in board direction (ft)

Deck width across the boards (ft)

Board width 5-1/2" (5/4x6, 2x6, most composite)3-1/2" (2x4)5-1/4"7-1/4" (2x8)

Gap between boards 1/8"3/16"1/4"None (wet wood that will shrink)

Board length you buy 8 ft10 ft12 ft16 ft20 ft

Joist spacing 12"16"24"

Extra for waste 5% (simple rectangle)10%15% (angles, picture frame)

Rows are rounded up, so the last board may need ripping to width. Screws assume 2 per board at each joist; hidden clips assume 1 per board at each joist. Always follow the decking maker's gap and spacing rules: many composite boards need 16" or even 12" joist spacing, and less for diagonal layouts.

Boards needed for common deck sizes

5-1/2" boards, 3/16" gap, boards running the long way, 10% extra.

How the calculation works

1. Rows of boards = deck width (in inches) ÷ (board width + gap), rounded up.
2. Linear feet = rows × deck length.
3. Boards to buy: each row gets as many full-length boards as fit, and the leftover piece is cut from extra boards, reusing offcuts only where they are long enough. Then add the waste allowance.
4. Joists crossed = deck length ÷ joist spacing + 1, and each board gets 2 screws (or 1 clip) per joist.

Engineer's note: pick board length to match your joist layout. Board ends must land on a joist, so on a 14 ft run with 16 ft boards you waste 2 ft per row. Doubling the joist where boards butt together gives each end its own bearing and avoids splitting. Check your joists can carry the span with the deck joist span calculator.

Common questions

How many deck boards for a 10x10 deck?

With 5-1/2" boards and a 3/16" gap, 22 rows of 10 ft boards, so about 25 boards with 10% extra.

How many screws per deck board?

Two at every joist. A 16 ft board over joists at 16" crosses 13 joists, so 26 screws. A 5 lb box of 2-1/2" deck screws holds roughly 350 to 450, depending on brand.

Which way should deck boards run?

Usually at right angles to the joists, often parallel to the house. Diagonal boards look good but need closer joist spacing (often 12") and about 15% extra material.

Checked by: Engr. Abdul Latif, civil and structural engineer. Quantities are geometry; follow your decking manufacturer's installation guide. Estimates for planning only.