Decking Calculator: Deck Boards, Linear Feet & Waste
Calculate how many deck boards you need based on deck size, board width, spacing, board length and waste.
Enter the deck dimensions and the actual dimensions of the decking being installed to estimate the number of board rows, total linear feet and full deck boards to order.
The calculator works with wood, composite and other straight deck boards. Add the price per board to estimate your primary decking material cost.
This calculator estimates the field decking only. Framing, stairs, fascia, railing, fasteners and other deck materials should be calculated separately.
Free Decking Calculator
Decking Calculator
Enter the deck dimensions and decking size to estimate board rows, linear feet and full boards needed.
This calculator estimates straight field decking from deck dimensions, board width, spacing and stock board length. Diagonal or patterned layouts, picture framing, breaker boards, stairs, fascia and unusual seam layouts can require additional material. Confirm the final board layout before ordering.
How Many Deck Boards Do I Need?
The number of deck boards depends on more than the total square footage of the deck. Board width and the planned gap between boards determine how many rows of decking are needed across the deck.
The calculator assumes the boards run in the direction entered as Deck Length. The Deck Width is the distance perpendicular to those boards.
Once the number of board rows is calculated, the calculator determines the total linear footage of decking required.
Use Actual Deck Board Width
For an accurate estimate, enter the actual face width of the decking rather than relying only on its nominal lumber size.
For example, a board commonly referred to as a 2 × 6 does not normally have an actual face width of 6 inches. Composite decking also varies by manufacturer and product.
Measure the board or use the manufacturer's actual dimensions and enter that width into the calculator.
How Does Board Spacing Affect the Estimate?
The gap between deck boards contributes to the total width covered by each row of decking.
The calculator accounts for both the board width and the spacing between adjacent boards when determining how many rows are required.
Use the planned installed spacing for the actual decking product. Required spacing can vary by material, manufacturer and installation conditions.
How Much Extra Decking Should I Order?
Decking estimates should normally include additional material beyond the theoretical minimum.
Extra decking may be needed for:
- End cuts
- Trimming
- Damaged or defective boards
- Seam layout
- Board selection
- Unusable offcuts
- Obstructions
- Future repairs
A 10% waste allowance is a useful estimating starting point for a straightforward deck, but the appropriate allowance depends on the layout.
Diagonal decking, picture-frame borders, complicated shapes and patterned installations can require additional material. Adjust the calculator's waste percentage for the actual project.
Decking Calculator Formula
The calculator first determines the deck area:
Deck Length × Deck Width = Deck Area
It then calculates the number of board rows using the deck width, actual board width and board spacing.
Board Rows × Deck Length = Base Linear Feet
The selected waste allowance is then added:
Base Linear Feet × (1 + Waste % ÷ 100) = Linear Feet With Waste
Finally:
Linear Feet With Waste ÷ Stock Board Length = Boards Needed
The final quantity is rounded up to the next whole board.
Decking Calculator Example
Suppose you're building a deck measuring:
20 feet long × 16 feet wide
The deck contains:
20 × 16 = 320 square feet
Assume the decking is 5.5 inches wide with a 1/4-inch gap between boards. The calculator determines that approximately 34 rows are needed across the 16-foot width.
Those rows require:
34 × 20 = 680 linear feet of decking
Adding 10% waste gives:
680 × 1.10 = 748 linear feet
If you're purchasing 16-foot boards:
748 ÷ 16 = 46.75 boards
The estimated order quantity is therefore:
47 deck boards
What Does This Decking Calculator Include?
This calculator estimates the primary field decking for a straight board layout.
It does not separately calculate:
- Joists
- Beams
- Posts
- Footings
- Ledger boards
- Stairs
- Railing
- Fascia
- Picture-frame borders
- Fasteners or hidden clips
- Concrete or hardware
Those materials depend on the deck design, structure and installation system and should be estimated separately.
Use Decking Cost to Build Your Estimate
Deck boards are only one part of a deck project. Contractors may also need to account for framing lumber, footings, hardware, fasteners, railing, stairs, delivery, equipment, disposal, labor and overhead.
Once you know the expected decking cost, use the Contractor Job Cost Calculator to build the rest of the job cost. Then use the Contractor Markup Calculator or Contractor Profit & Margin Calculator to check your selling price and expected profitability.
Frequently Asked Questions
How do I calculate how many deck boards I need?
Determine how many board rows are required across the deck using the actual board width and spacing. Multiply the rows by the length the boards run to determine linear footage, add waste, then divide by the stock board length.
Should I use nominal or actual deck board width?
Use the actual face width of the installed decking. Nominal lumber dimensions may not match the board's actual measurements.
Does the gap between deck boards matter?
Yes. The spacing between boards contributes to the total width covered by the decking and therefore affects the number of board rows required.
How much waste should I add for decking?
Ten percent is a useful starting point for many straightforward layouts, but the appropriate amount depends on board lengths, cuts, seam layout, deck shape and installation pattern.
Can I use this calculator for composite decking?
Yes. Enter the actual width, planned spacing and stock length of the composite board being installed. Follow the manufacturer's installation requirements for spacing and layout.
Does this calculator include deck framing?
No. It estimates the field decking only. Joists, beams, posts, footings, hardware, stairs, railing and other structural materials should be calculated separately.