Free tool
Deck Calculator
Enter your deck dimensions, board size, length, and gap and get exactly how many decking boards you need — plus linear feet and a material-cost ballpark. Free, no signup.
Decking needed
0 boards
- Deck area0 ft²
- Coverage per board0 ft²
- Boards needed0
- Linear feet of decking0 ft
- Estimated cost$0
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Or download it now (PDF)How to calculate how many deck boards you need
Decking is bought by the board but installed across an area, so the whole take-off comes down to one thing: how much deck a single board covers once you account for the gap between boards. Get the gap or the units wrong and the count drifts, so this is the step to slow down on.
1. Find the deck area
Deck area is length × width in feet. For an L-shaped or multi-level deck, break it into rectangles, calculate each, and add them together.
2. Work out coverage per board
Each board’s effective width is its face width plus the gap you leave between boards. A 5.5-inch board with a 1/8-inch gap effectively occupies 5.625 inches, or 0.469 ft. Multiply that by the board length to get square feet per board. The calculator does this the moment you pick a board size and length.
3. Divide, add waste, and round up
Divide deck area by coverage per board, add your waste percentage, and round up to a whole board — you cannot buy a partial. Straight runs use about 10%; diagonal or picture-frame patterns leave bigger offcuts, so bump waste to 15% or more.
4. Convert to linear feet if your yard prices that way
Linear feet is the board count times the board length. Many lumber yards quote decking per linear foot, so the calculator shows both — order by the number that matches your supplier’s pricing.
Sizing the decking is step one. Turning it into a priced, professional quote is faster inside CrewRivet. See the fence calculator, the flooring calculator, or the job pricing calculator.
Deck calculator FAQ
- How many deck boards do I need?
- Divide your deck area (length × width in feet) by the coverage of a single board, then round up. A board’s coverage is its face width plus the gap between boards, converted to feet, times the board length. A 5.5-inch board run at 16 ft with a 1/8-inch gap covers about 7.5 sq ft, so a 200 sq ft deck needs roughly 27 boards before waste. This calculator does the width-plus-gap math for you and adds your waste percentage.
- What gap should I leave between deck boards?
- A 1/8-inch (0.125") gap is the common default for pressure-treated and composite boards installed when dry; some builders run boards tight (green pressure-treated lumber shrinks as it dries) or up to 1/4 inch for drainage. The gap matters because it reduces how many boards you need — a wider gap means each board covers more deck. Enter your planned gap and the calculator factors it in.
- How much extra decking should I order for waste?
- Order about 10% over the bare calculation for straight-run decks, and more — 15% or higher — for diagonal, herringbone, or picture-frame patterns where cuts leave larger offcuts. Waste also covers defective boards and mistakes. The default here is 10%; bump it up for angled layouts.
- How do I figure linear feet of decking?
- Linear feet is simply the number of boards times each board’s length — it is how lumber yards often price and sell decking. If you need 27 boards at 16 ft, that is 432 linear feet. The calculator shows both the board count (what you carry) and the linear footage (how it is often quoted) so you can order either way.
- Is this deck calculator free?
- Yes — the live estimate is free with no email required. Enter your email only if you want the free Job Pricing Kit (pricing worksheet, markup cheat-sheet, and invoice + quote templates) sent to your inbox.