How to Use the Deck Board Calculator

Use the Builzee deck board calculator to estimate how many decking boards and how much total linear footage you need for a deck surface.

Start by entering the finished length and width of each rectangular deck section. For irregular or multi-level decks, divide the project into separate rectangles and use Add Another Deck Section.

For each section, choose the direction the decking boards will run. Then enter or select:

• actual board width
• gap between boards
• stock board length
• waste allowance

The calculator estimates the number of board courses, total decking length and approximate number of stock boards to purchase.

Measure the Finished Deck Surface

Measure the length and width of the area that will actually be covered with decking.

For a simple rectangular deck measuring 20 feet by 12 feet:

20 × 12 = 240 square feet

Square footage is useful for understanding the overall deck size, but decking quantity also depends on board width, spacing and the direction the boards run.

For an L-shaped or irregular deck, divide the surface into rectangular sections and enter each section separately.

Choose the Direction the Deck Boards Will Run

Board direction matters because it determines the length of each board course and how many courses are required across the deck.

For example, on a 20-foot × 12-foot deck:

Along Deck Length means the boards run in the 20-foot direction.

Along Deck Width means the boards run in the 12-foot direction.

Changing the direction can slightly change total linear footage because the number of board courses must be rounded up to fully cover the deck.

Board direction also needs to work with the actual framing below. Deck boards normally run perpendicular to the supporting joists.

Use the Actual Deck Board Width

Decking is often described using nominal dimensions that are different from the actual finished board width.

For example, a nominal 1 × 6 or 5/4 × 6 wood deck board may have an actual face width around 5.5 inches.

Composite and PVC decking dimensions can vary by manufacturer.

The calculator uses the actual installed face width because that is what determines how many board courses are needed across the deck.

If your decking does not match one of the preset widths, choose Custom and enter the actual board width.

Account for the Gap Between Deck Boards

Deck boards are normally installed with a gap between adjacent boards.

The correct gap depends on the decking material, moisture condition and manufacturer’s installation requirements.

Common spacing may include:

• 1/8 inch
• 3/16 inch
• 1/4 inch

The calculator combines the board width and gap to determine the effective coverage of each board course.

For example:

5.5-inch board + 3/16-inch gap = 5.6875 inches of effective coverage

Always follow the spacing instructions for the specific decking product you are installing.

How the Calculator Determines Board Courses

The calculator determines how many rows of decking are required across the dimension perpendicular to the board direction.

Because you cannot normally install a fraction of a board course, the result is rounded up to the next full course.

For example, if a deck requires approximately 25.4 courses, the calculator plans for:

26 board courses

The final course may need to be ripped narrower during installation to fit the remaining space.

Understanding Linear Feet of Decking

Decking material is useful to think about in linear feet as well as square footage.

If a project requires 26 board courses and each course runs 20 feet:

26 × 20 = 520 linear feet of decking

The calculator first determines the linear footage required before waste.

It then applies the selected waste allowance before estimating the number of stock boards to purchase.

Choosing a Stock Board Length

Deck boards are sold in standard lengths, commonly including:

• 8 ft
• 10 ft
• 12 ft
• 16 ft
• 20 ft

Availability varies by material and manufacturer.

Choose the length you actually plan to purchase.

The calculator divides the required linear footage by the selected stock length and rounds up to the next whole board.

For example:

520 linear ft ÷ 16 ft = 32.5 boards

You would need at least:

33 boards

This is a material-planning estimate. Actual joint locations and usable offcuts can affect the final quantity.

How Much Waste Should You Add for Decking?

Deck installations rarely use every piece of material perfectly.

Extra decking may be needed for:

• end cuts
• damaged boards
• defects
• board staggering
• trimming
• irregular deck edges
• unusable offcuts
• layout adjustments

The calculator uses 10% waste as the standard setting.

A simple rectangular deck using straight boards may require less.

More complex projects may need additional waste, especially when using:

• diagonal decking
• picture-frame borders
• breaker boards
• complicated corners
• multiple deck levels

Use the waste setting that best matches the project layout.

Picture-Frame Borders and Breaker Boards

Many modern decks use picture-frame boards around the perimeter or breaker boards through the middle of the deck.

These details are not automatically calculated because their quantities depend on the exact deck layout.

The main calculator estimates the field decking.

If your design includes picture framing or breaker boards, calculate those pieces separately and consider increasing the waste allowance for additional cuts.

This is especially important when working with composite decking where layout and seam placement may be planned around specific stock lengths.

What About Diagonal Decking?

Boards installed diagonally generally create more cutting waste than straight decking.

The calculator can still estimate the basic decking quantity, but the exact material requirement depends heavily on the deck shape and diagonal angle.

For diagonal layouts, use a larger waste allowance than you would for a simple straight-board installation.

Do not rely on the standard 10% allowance automatically for a complicated diagonal design.

Calculating Multiple Deck Sections

Use Add Another Deck Section for decks with separate rectangular areas.

This is useful for:

• L-shaped decks
• multi-level decks
• side extensions
• landings
• separate deck platforms

Each section can have its own dimensions, board direction and quantity.

For identical areas, the Qty field allows you to repeat the same section without entering it multiple times.

The calculator combines the decking requirements for all sections before applying the project waste allowance.

What the Deck Board Calculator Does Not Include

This calculator is designed specifically for the finished decking surface.

It does not calculate:

• joists
• beams
• posts
• footings
• concrete
• railings
• stairs
• fascia
• fasteners
• hidden clips
• hardware
• labor or cost

Those items depend on structural design, local code requirements and the specific decking system being used.

Before You Order Decking

Verify the deck dimensions and planned board direction before purchasing material.

Also confirm:

• actual board width
• required board spacing
• available stock lengths
• manufacturer installation instructions
• planned seams and joints
• picture-frame or breaker-board details
• stair and fascia requirements

For composite or proprietary decking systems, check the manufacturer’s installation guide before finalizing quantities.

A small amount of leftover decking can also be useful for future repairs or replacement boards.