Deck Calculator
Enter your deck size and board width to see how many deck boards you need — plus total linear feet, a buy-list by stock length, joists, and screws.
You need · incl. +10% waste
- Deck area
- 192 ft²
- Exact decking
- 416 lin ft
- Joists
- 13
- Joist material
- 156 lin ft
Boards to buy by stock length
Board counts include a 10% waste allowance. Linear feet is what lumberyards price from; the buy-list shows how many boards at each stock length.
The formula & specs
Rows = Deck width ÷ (board width + gap). Decking linear feet = Rows × deck length. Boards to buy = Linear feet ÷ stock length, rounded up, plus a waste allowance.
| Board face widths (actual) | 5.5" · 5.25" · 3.5" |
| Board gaps | 1/8" · 3/16" · 1/4" |
| Joist spacing (on-center) | 12" · 16" · 24" |
| Board stock lengths | 8 ft · 10 ft · 12 ft · 16 ft · 20 ft |
Nominal board sizes differ from actual: a “6-inch” board is 5.5" wide. The calculator uses actual widths so the row count matches your real material.
How to estimate deck materials
The number of deck boards comes down to one ratio: how many board widths fit across your deck. Each board covers its face width plus the gap between boards, so a "6-inch" board (actually 5.5 inches) at a 1/8-inch gap occupies about 5.625 inches. Divide the deck width by that and round up, and you have the number of rows. Multiply by the deck length and you have the total linear feet of decking — the number lumberyards actually price from.
Gaps and board width matter more than people expect. Pressure-treated boards go down tight (1/8 inch) because they shrink as they dry; dry or composite boards need 1/8–1/4 inch so they have room to move with temperature. Get the gap wrong and you either trap water and debris or end up with gaps wide enough to lose a phone through. The calculator lets you set the exact board width and gap so the row count matches your real material.
Buy by stock length, not just linear feet. A lumberyard sells 8, 10, 12, 16, and 20-foot boards — the calculator shows how many of each you would need so you can pick the length that wastes the least and minimizes butt joints. It also estimates joists (at your on-center spacing) and the face screws to fasten the deck, so you can price the whole job, not just the boards. Always add ~10% for cuts, waste, and the occasional bad board — 15% for a diagonal pattern.
Frequently asked questions
How many deck boards do I need?+
Divide your deck width by the board width plus the gap to get the number of rows, then multiply by the deck length for total linear feet. Divide that by your board stock length (8–20 ft) and round up. Enter your deck size and board width above and the calculator does all of it, including a buy-list by stock length.
How do I calculate linear feet of decking?+
Linear feet = number of board rows × deck length. The rows are your deck width divided by the board face width plus the gap, rounded up. For a 16 ft × 12 ft deck with 5.5-inch boards and a 1/8-inch gap, that is about 26 rows × 16 ft = 416 linear feet before waste.
How many deck boards in a 12×16 deck?+
About 26 rows of decking, roughly 416 linear feet — which is around 29 boards if you buy 16-foot stock, including a 10% waste allowance. Change the board width, gap, and stock length above to match your material for an exact count.
What gap should I leave between deck boards?+
Lay pressure-treated boards tight (about 1/8 inch) because they shrink as they dry. Install kiln-dried or composite boards with a 1/8–1/4 inch gap so they can expand and contract. A gap keeps water and debris from collecting and lets the deck breathe.
What is the actual width of a deck board?+
A nominal "6-inch" deck board (5/4×6 or 2×6) is actually 5.5 inches wide; a "4-inch" board is 3.5 inches. Composite boards are often 5.25–5.5 inches. The calculator uses actual widths because that is what determines how many fit across your deck.
How far apart should deck joists be?+
Most decks use 16-inch on-center joist spacing. Use 12-inch spacing for extra stiffness or when boards run diagonally, and 24-inch only if your decking and span tables allow it. Set the spacing above and the calculator estimates the number of joists and their linear feet.
How many screws do I need for a deck?+
For face-screwed boards, plan on about 2 screws per board at every joist it crosses. The calculator multiplies your board rows by the number of joists by 2 — for a typical 12×16 deck at 16-inch spacing that is roughly 676 screws. Hidden-fastener systems use their own clip counts.
How much extra decking should I order?+
Add about 10% to the linear feet for cuts, waste, and the odd unusable board. For a 45-degree diagonal pattern, add about 15% because the angled cuts waste more. The calculator includes an adjustable overage and a diagonal option.
What length deck boards should I buy?+
Buy the stock length that spans your deck with the fewest joints and least offcut — the calculator shows the board count for 8, 10, 12, 16, and 20-foot lengths so you can compare. A 16-foot deck is most efficient with 16-foot boards; odd dimensions sometimes waste less in two shorter lengths.
Does a diagonal deck pattern use more boards?+
Yes — a 45-degree pattern wastes roughly 15% more material because of the angled end cuts, and it usually needs tighter (12-inch) joist spacing. Toggle the diagonal option above and the calculator adds the extra material automatically.
Is this deck calculator free?+
Yes — it is completely free, needs no sign-up, and runs entirely in your browser, so nothing you enter is stored or sent anywhere.