Deck Material Calculator
A free deck material calculator that estimates deck boards, joists, and screws together for a simple rectangular deck — enter your measurements once and get every quantity in one place, plus optional cost.
Free Instant No signup required
Your Estimate
- Deck Area
- —
- Deck Board Rows
- —
- Boards Needed Before Waste
- —
- Boards Including Waste Order this many
- —
- Total Decking Linear Feet
- —
- Approximate Joist Count
- —
- Approximate Deck Screw Count
- —
- Suggested Screw Boxes
- Enter screws per box to estimate box quantity
- Estimated Decking Cost
- Enter a price to estimate this cost
- Estimated Screw Cost
- Enter a price to estimate this cost
- Combined Estimated Material Cost
- Enter a board or box price to estimate combined cost
Board-to-board joints must be properly supported according to the decking manufacturer’s installation instructions and applicable local building requirements.
Estimates only. This calculator estimates material quantities only. Framing sizes, structural requirements, spans, connections, and permit requirements must be verified separately. Read the full disclaimer.
How to Use the Deck Material Calculator
Use this deck materials calculator once you have a deck size in mind. Enter your deck size and board specs, then joist spacing and screws per crossing. The three optional cost fields at the bottom are independent of each other — fill in as many as you know.
- Deck length and deck width
- The finished size of the deck surface. Boards run along the length; rows stack across the width.
- Deck board length and width
- The stock board size you plan to buy. Use the actual width, not a nominal lumber size.
- Board gap / spacing
- The gap between boards, in inches. Presets cover 1/8″, 3/16″, and 1/4″.
- Waste percentage
- An allowance for cuts and mistakes, applied to the decking board count.
- Joist spacing and screws per intersection
- Drive the approximate joist and screw counts. 16″ joist spacing and 2 screws per crossing are common defaults.
- Optional prices
- A board price, a screw box size and price, or both — the calculator adds whichever you provide into a combined cost.
What Deck Materials Does This Calculator Estimate?
As a decking material calculator, this V1 tool covers three material categories for a simple rectangular deck:
- Decking boards — rows, board count before and after waste, and total linear feet.
- Joists — an approximate count based on deck length and joist spacing.
- Screws — an approximate fastener count from joist crossings and board count, with an optional box suggestion.
This calculator estimates material quantities only. Framing sizes, structural requirements, spans, connections, and permit requirements must be verified separately. It does not calculate or recommend beam sizing, post sizing, footing sizing, structural spans, load capacity, ledger requirements, structural connections, or permit and code compliance.
For those, consult a licensed contractor or engineer and your local building department before buying materials or starting construction.
How Many Deck Boards Do I Need?
Rows come from your deck width, board width, and gap; board count comes from your deck length and board length. Both use the same row-and-piece method as the deck board calculator and the composite deck board calculator.
Board formulas
- Rows = (deck width + gap) ÷ (board width + gap), rounded down to the number that fits
- Full boards per row = deck length ÷ board length, rounded down
- Leftover run = deck length − (full boards × board length)
- Pieces from one board = board length ÷ leftover run, rounded down
- Boards before waste = (rows × full boards per row) + (rows ÷ pieces per board, rounded up)
- Boards including waste = boards before waste × (1 + waste percentage), rounded up
- Total linear feet = boards including waste × board length
Rows round down, not up, because the deck width is a fixed boundary you can't exceed — rounding up can claim more physical boards side by side than the width can actually hold. When the gap you entered doesn't divide the width evenly, the results explain the exact spacing that uses the full width with nothing left over. Offcuts are reused only when one leftover piece is long enough to finish another row on its own — short scraps are never combined to make up a run.
How Many Joists Do I Need?
Joists run across the deck width, spaced along the deck length, and every row of decking shares the same joists — so joist count depends only on deck length and joist spacing, not on deck width or board width.
Joists (approximate) = deck length ÷ joist spacing, rounded down, plus one for the starting joist.
| Joist spacing | Approximate joists |
|---|---|
| 12″ on-center | 13 |
| 16″ on-center | 10 |
| 24″ on-center | 7 |
This is a material estimate only, not a structural calculation. It does not imply the resulting joist count, size, or spacing is structurally adequate for your deck. Real framing can add blocking, doubled joists, or a ledger-side starting point. Actual joist size and spacing depend on span tables, load requirements, and your local building code — verify these separately with a qualified professional.
How Many Deck Screws Do I Need?
Screw count reuses the same joist-crossing method as the dedicated deck screw calculator, applied automatically from your deck length instead of a manually entered board count.
Screw formulas
- Screws per board = approximate joist count × screws per intersection
- Total screws (approximate) = boards before waste × screws per board
- Suggested boxes = total screws ÷ screws per box, rounded up
Screw count uses the boards-before-waste figure, not the boards-including-waste figure — extra boards bought for cuts and mistakes generally don't get installed, so they don't get screwed down either.
Deck Material Waste Allowance
The waste percentage applies to decking boards — it covers saw kerf, end trims, offcuts too short to place, and the occasional bad cut.
- Around 10% — a simple rectangle, boards running one direction, few obstructions.
- Around 15% — awkward dimensions, a few posts to cut around, or a first deck build.
- 15–20% or more — diagonal installs, picture-frame borders, stairs, or multi-level decks.
On the 12 by 10 foot example below, 21 boards before waste becomes 24 boards at 10%, or 25 boards at 15%. Joist and screw counts are not affected by the board waste percentage.
Example Deck Material Estimate
A 12 ft by 10 ft deck: 12-foot boards, 5.5 inches wide, spaced 1/8 inch apart, 10% waste, 16 inch joist spacing, 2 screws per intersection.
- Deck area: 12 ft × 10 ft = 120 sq ft
- Rows: (120 + 0.125) ÷ 5.625 = 21.36 → rounded down to 21 rows
- Boards before waste: 21 × 1 board per row = 21 boards
- Boards including 10% waste: 21 × 1.10 = 23.1 → 24 boards
- Total linear feet: 24 × 12 ft = 288 linear ft
- Joists: (12 ft × 12) ÷ 16 = 9 → + 1 = 10 joists
- Screws per board: 10 × 2 = 20 screws
- Total screws: 21 boards × 20 = 420 screws
Add $4.75 per board and the estimated decking cost comes to $114.00 (24 × $4.75). Add 100 screws per box at $8.99 and that's 5 boxes (420 ÷ 100, rounded up) for $44.95 — a combined estimated material cost of $158.95.
Frequently Asked Questions
How much deck material do I need?
It depends on your deck's size and your board, joist, and screw specs, but the pieces are the same for any rectangular deck: board rows from your deck width and board width, board length from your deck length, joists from your deck length and joist spacing, and screws from joist crossings times boards.
A 12 ft by 10 ft deck with 5.5 inch boards, 1/8 inch spacing, 16 inch joist spacing, and 2 screws per intersection needs 21 rows, 24 boards with 10% waste, 10 joists, and about 420 screws.
How many deck boards do I need?
Divide your deck width by the actual board width plus your spacing gap to get the number of rows, then work out how much board length each row needs from your deck length and board length.
This calculator rounds rows down to the number that actually fits your deck width, then rounds the final board count up so you never buy a fractional board.
How many joists do I need for a deck?
As an approximate material estimate: divide your deck length by your joist spacing and add one for the starting joist.
This is not a structural calculation — actual joist count, size, and spacing depend on your span tables, load requirements, and local building code, and must be verified separately.
How many deck screws do I need?
Multiply your approximate joist count by the screws used at each joist crossing, then multiply by your board count.
This uses the same joist-crossing method as the dedicated deck screw calculator, applied automatically from your deck dimensions instead of a manually entered board count.
Does this calculator check structural requirements?
No. This calculator estimates material quantities only — decking boards, an approximate joist count, and fasteners.
It does not calculate or recommend beam sizing, post sizing, footing sizing, structural spans, load capacity, ledger requirements, structural connections, or permit and code compliance. Verify all framing and structural requirements separately with a qualified professional and your local building department.
Can I price out my whole deck here?
You can estimate decking and screw costs. Enter a price per board for an estimated decking cost, and screws per box plus a box price for an estimated screw cost — the calculator adds both into a combined material cost.
As a deck material estimator, it does not price framing lumber, hardware, footings, or labor. For board quantities only, see the deck board calculator; for even spacing, see the deck board spacing calculator; for composite-specific defaults, see the composite deck board calculator.
Disclaimer
The results produced by DeckBoardEstimator.com are estimates only, intended for general planning purposes. This calculator estimates material quantities only. Framing sizes, structural requirements, spans, connections, and permit requirements must be verified separately.
It does not calculate or recommend beam sizing, post sizing, footing sizing, structural spans, load capacity, ledger requirements, structural connections, or permit and code compliance, and it is not a substitute for engineered plans or a permit set.
Always double-check your own measurements, confirm product dimensions and installation requirements with your supplier and manufacturer, and verify structural and permit requirements with your local building department and applicable building codes before purchasing materials or beginning construction. For structural questions, consult a licensed contractor, engineer, or building official.
DeckBoardEstimator.com makes no warranty as to the accuracy of these calculations and accepts no liability for any loss, cost, or damage arising from their use.