How many deck boards do I need for 200 square feet?

With 5.5 in × 8 ft boards (3.667 sq ft coverage) and 10% waste: 200 × 1.10 ÷ 3.667 = 60 boards.

How do I calculate deck board coverage?

Coverage = (board width in inches ÷ 12) × board length in feet. A 5.5 in × 8 ft board covers 3.667 sq ft. Then boards = area × (1 + waste) ÷ coverage.

How much waste should I add for decking?

10% for a straight rectangular deck, 15% for a diagonal or picture-frame layout, and 15–20% for complex or herringbone decks — the gap between boards and end cuts add up.

How many screws do I need for a deck?

Roughly 350 screws per 100 sq ft for face-screwed boards (two per joist crossing at 16 in spacing). Confirm against your fastener box; hidden-fastener systems list their own coverage.

What is the actual width of a deck board?

A nominal 5/4×6 or 2×6 board is really 5.5 in wide. Always use the actual width, not the nominal, when counting boards.

How much decking do I need (boards & fasteners)?

Deck boards come from two numbers: the deck area and the coverage of one board (its width × length). Divide, add waste for cuts and the gap between boards, and round up.

By Francesco Zinghinì

The deck-board formula

Each board covers its own footprint — width times length — so the count is area over coverage, plus waste:

board coverage = (board width (in) ÷ 12) × board length (ft)
boards = area (sq ft) × (1 + waste) ÷ board coverage, rounded up

A nominal 5/4×6 or 2×6 deck board is actually 5.5 in wide. The deck-boards tool takes your board size and waste and returns the count — use the actual width, not the nominal.

Worked example: 200 sq ft, 5.5 in × 8 ft boards

Coverage = (5.5 ÷ 12) × 8 = 0.458 × 8 = 3.667 sq ft per board.
Boards = 200 × 1.10 ÷ 3.667 = 220 ÷ 3.667 = 60.0, rounded up to 60 boards (10% waste).

The board coverage here is the nominal footprint. In practice you leave a small gap between boards for drainage and expansion, which the waste allowance comfortably absorbs — that is one reason decking uses a higher waste figure than mulch or gravel.

Why decking needs more waste

Deck boards waste more than most materials because of the gap between boards, the trimming to length at the ends, the pattern (a diagonal or herringbone deck wastes far more than a straight run), and the picture-frame border many decks use. Plan for:

10% waste — a straight, rectangular deck.
15% waste — a diagonal layout or a picture-frame border.
15–20% waste — complex shapes, multiple levels, or a herringbone.

Fasteners

Fastener counts follow the joist spacing: each board is fastened at every joist it crosses. With joists 16 in on center, a board crosses a joist roughly every 16 inches of its length, and you use two screws per crossing for face-screwed boards (hidden-fastener systems have their own per-square-foot coverage on the box). As a rough planning figure, budget about 350 screws per 100 sq ft of decking, then confirm against the fastener box coverage.

Don’t forget the substructure and footings

The boards are the visible layer; below them are joists, beams, posts and footings. Post footings are set in concrete — size the concrete per hole with the post-hole concrete tool, the same math a fence uses. Framing spans, footing depth and ledger attachment are structural and code-driven; confirm them against your local code and, for anything raised or attached to the house, a permit.

Board length and layout waste

Deck boards come in set lengths (commonly 8, 12 and 16 ft), and matching the board length to your deck dimension cuts waste hard. A 12 ft-wide deck floored with 12 ft boards has almost no end-cut waste; the same deck in 16 ft boards throws away 4 ft off every board unless you can use the offcut elsewhere. Where a run is longer than the board, plan the butt joints to fall on a joist and stagger them so seams do not line up. A diagonal layout looks great and stiffens the deck, but every board meets the rim at an angle and wastes more — which is why diagonal decks jump to the 15% waste band.

Quick reference: boards by deck size (5.5 in × 8 ft, 10% waste)

Each board covers 3.667 sq ft; boards = area × 1.10 ÷ 3.667:

100 sq ft → about 30 boards.
200 sq ft → 60 boards.
300 sq ft → about 90 boards.
400 sq ft → about 120 boards.

Composite and PVC boards use the same coverage math — just enter their actual width and length; many run 5.5 in wide like wood.

Common decking mistakes

Using the nominal width. A “6-inch” board is 5.5 in — using 6 undercounts the boards.
Forgetting the gap. The small gap between boards for drainage is real coverage; the waste allowance absorbs it, so do not also add it separately.
Mismatched lots. Composite color varies by production run — buy all the decking, including waste, at once.
Ignoring the substructure. Boards are the easy part; joists, beams, footings and ledger attachment are structural and code-driven.

Once you have the board and fastener counts, estimate the spend with the deck cost tool from your own $/sq ft. Every count here is a coverage estimate: confirm the actual board width, account for the gap and pattern, and buy 10–20% extra so you are not short mid-project or matching a different lot later.

Key takeaways

Board coverage = (board width in ÷ 12) × board length ft; boards = area × (1 + waste) ÷ coverage.
A 5.5 in × 8 ft board covers 3.667 sq ft — use the actual width, not the nominal.
200 sq ft at 10% waste needs 60 boards; budget about 350 screws per 100 sq ft face-screwed.
Match board length to the deck dimension to cut end-cut waste; diagonal layouts waste more (15%).
Boards are the easy part — joists, footings and ledger attachment are structural and code-driven.