Deck Calculator
Deck boards, linear feet and screw count for a rectangular deck.
Quick answer
- Formula: Boards = ceil(Deck width (in) ÷ (board width + gap)); Screws = Boards × (floor(Length (in) ÷ joist spacing) + 1) × 2
- Worked example — Boards needed: 26 (full example below).
Deck Calculator
| Boards needed | 26 |
| Length of each board | 16 ft |
| Total decking | 416 linear ft |
| Joist crossings per board | 13 |
| Screws (2 per crossing) | 676 |
A 16 × 12 ft deck with 5.5 in boards and a 1/8 in gap needs 26 boards (416 linear feet). Each board crosses 13 joists, so at 2 screws per crossing you need about 676 screws.
This calculator assumes the deck boards run along the deck's length. It divides the deck width by the board width plus a 1/8-inch gap between boards to count the boards, rounds UP to whole boards, and totals the linear feet of decking to order.
Board widths are actual widths: a nominal 2×6 deck board is really 5.5 inches wide and a 2×4 is 3.5 inches. The screw estimate uses 2 screws at every joist crossing — with joists at the standard 16 inches on center, a board crosses a joist every 16 inches of its length, plus one at the end.
The formula
Worked example
A 16 × 12 ft deck with 5.5 in boards and a 1/8 in gap needs 26 boards (416 linear feet). Each board crosses 13 joists, so at 2 screws per crossing you need about 676 screws.
The example is pre-loaded in the result panel — press Calculate with your own numbers to replace it.
Frequently asked questions
How much extra decking should I buy?
Order about 10% more linear feet than the exact figure to cover end cuts, board defects and mistakes — more for diagonal patterns. Boards are counted whole here, which already builds in a small surplus.
Why use actual board width instead of nominal?
A '2×6' is milled down to 1.5 × 5.5 inches. Laying out with the nominal 6-inch width would leave you about half a board short across a typical deck width.
What gap should I leave between boards?
About 1/8 inch for kiln-dried or composite boards and up to 1/4 inch for pressure-treated lumber that will shrink as it dries. Many builders use an 8d nail or a spacer as a gauge.
Category: Construction & Home calculators
Sources & methodology
This calculator applies the formula shown on this page exactly as written, using the standard definitions for its inputs. Results are computed from the values you enter — no data is stored — and are rounded only for display.
Content last reviewed by CalcHub Editorial.
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