Deck Calculator
Enter the deck's length and width, pick your decking board and joist spacing, and the calculator returns the three things you build a deck from: the decking boards to surface it, the joists to frame it, and the deck screws to fasten everything down. Boards run the length and cross the joists, which span the width.
Your measurements
The direction the decking boards run.
The direction the joists span (out from the house).
The face width of one decking board — how much it covers. A "2×6" actually measures 5.5 in wide.
Distance between joists, center to center. 16" is standard; 12" for stronger decks or diagonal boards; 24" only with thick composite.
The length of decking boards you'll buy. Match it to your deck length to cut waste — 16 ft is common.
Decking boards
29
16 ft each
Joists
13
16" o.c.
Deck screws
2 boxes
≈ 676
What to buy
- Decking boards — 16 ft
- 29 boards
- Joists
- 13 joists
- Deck screws
- 2 boxes(≈ 350/box)
26 rows of 5.5" board running the 16 ft length, plus 10% for cuts and a border.
The framing boards under the deck, spaced 16" apart on center. Each spans the 12 ft width.
About 676 screws — two at every spot a board crosses a joist.
Estimates only. Verify against your supplier's coverage figures before ordering.
Footprint
Deck framing to scale
13 joists @ 16" o.c. · 26 board rows
The numbers
- Deck area
- 192 ft²
- Board rows
- 26 rows
- Decking length
- 416 lin ft(before waste)
- With waste (+10%)
- 458 lin ft
- Joist run total
- 156 lin ft
Deck width ÷ (board width + 0.125" gap), rounded up.
Total running feet of decking — every row added end to end.
Divided by the 16 ft board length and rounded up, that's the 29 boards above.
13 joists × 12 ft — the framing lumber to buy by the foot.
The formula
Board rows = ⌈width ÷ (board + gap)⌉ · Decking = rows × length × (1 + waste) · Boards = ⌈decking ÷ stock length⌉ · Joists = ⌊length ÷ spacing⌋ + 1
Example: A 16 × 12 ft deck (192 ft²) with 5.5" boards at 16" o.c. needs about 26 board rows — roughly 29 sixteen-ft boards with 10% waste — plus 13 joists and 2 boxes of screws.
How it works
- 1Decking boards run the length of the deck, stacked in rows across the width. Rows = deck width ÷ (board face width + the gap between boards), rounded up.
- 2Total decking = rows × deck length, plus ~10% for cuts, the border and the odd bad board; divide by your board length and round up for the board count.
- 3Joists span the width and are spaced along the length: joists = length ÷ spacing (12, 16 or 24 in on center) + 1 for the closing joist.
- 4Deck screws: about two at every point a board crosses a joist — roughly 350 per 100 ft², sold by the box.
- 5This covers the deck surface and floor framing; add posts, beams, footings, railing and stairs separately for a full build.
Frequently asked questions
How many deck boards do I need?
Divide the deck width by the board's coverage (face width plus the gap) to get the number of rows, multiply by the deck length for total linear feet, add about 10% for waste, then divide by your board length. A 16 × 12 ft deck in 5.5-inch boards needs roughly 26 rows — about 29 sixteen-foot boards with waste.
What spacing should deck joists be?
16 inches on center is standard for most decks. Use 12 inches for a stiffer deck, for diagonal decking, or where the maker requires it; 24 inches is only allowed with thick composite or heavy decking rated for that span. Tighter spacing means a stronger, less bouncy deck.
How much extra decking should I buy for waste?
Add about 10% for a standard straight layout to cover end cuts, a picture-frame border, and defective boards. Bump it to 15% for diagonal or herringbone patterns, where angled cuts waste more material.
How many screws do I need for a deck?
Plan on about 350 deck screws per 100 square feet — roughly two screws at every spot a board crosses a joist. A 200 ft² deck needs around 700 screws, or two boxes. Hidden-fastener systems use clips instead and are counted per board.