Calculate Deck Board & Materials

How do I measure a deck?

Deck boards always run perpendicular to the joists. The length of the deck is measured in the same direction the deck boards run, which is usually along the side where the deck meets the house. The width is measured perpendicular to the length, or parallel with the joists, and determines how many deck boards you’ll need.

Use a tape measure to measure the deck framing in both directions. When measuring for board length, account for how the decking will meet the fascia. Deck boards may end flush with the side joists, with fascia covering the ends of the boards, or the boards may extend past the framing with the fascia installed below. Also account for any perimeter or picture-frame boards. If your design includes them, subtract their width from the dimensions of the field decking before calculating the length and number of boards needed.

How to Calculate Decking for Complex Deck Shapes

If your deck isn’t a simple rectangle, you can often divide it into two or more rectangular areas to calculate the decking you’ll need. Measure each area separately and enter the dimensions of each section into the decking board calculator. Add the results together to estimate the total decking needed for the project.

Deck Board Size and Spacing Considerations

Deck board width, length, and the gaps between boards all affect the amount of materials you will need. Understanding common board sizes and spacing can help you estimate materials more accurately and make more efficient use of available board lengths.

Deck Board Widths and Gaps

Most wood, composite, and PVC decking is sold in nominal 4-inch or 6-inch widths. A nominal 4-inch deck board is typically 3.5 inches wide, while a nominal 6-inch board is typically 5.5 inches wide.

Gaps between boards allow water to drain and give the decking room to expand and contract. Gap size varies depending on the decking material and fastening system. For example, hidden fasteners for composite decking commonly provide gaps of about 3/16 to 1/4 inch. Pressure-treated wood can require less initial spacing because it shrinks as it dries. Some installers use gaps of about 1/8 inch, while very wet pressure-treated boards may be installed tightly together and allowed to develop gaps as they dry.

This calculator uses the nominal board width to determine board count. Because the actual board width plus a typical gap is usually slightly less than the nominal width, the calculator adds one extra board to the estimate. Add another board when using 4-inch boards on decks wider than 14 feet or 6-inch boards on decks wider than 22 feet.

Deck Board Lengths

Wood decking is commonly available in lengths ranging from 8 to 20 feet in 2-foot increments, although available sizes vary by species and retailer. Composite and PVC decking is commonly offered in lengths of 8-foot, 12-foot, 16-foot, and 20-foot boards. When planning a new deck, sizing its length at or just under a commonly available board length can reduce waste and save money. On decks longer than the available board lengths, a divider board can eliminate visible butt joints by splitting the decking into two or more sections.

Deck Board Thickness

Wood decking is commonly available as 5/4-inch or nominal 2-inch material, while composite and PVC board thicknesses vary by manufacturer and product line. Board thickness can affect strength, how a deck feels underfoot, and allowable joist spacing, but it does not affect the number of deck boards required to cover a given area.

Orientation of the Decking

The direction and pattern of your deck boards affect the appearance of the deck as well as the amount of material you’ll need. Deck boards must be supported by joists at the proper spacing for the material and installation angle you choose. Always follow the decking manufacturer’s installation requirements and local building codes.

Deck Boards Installed 90° to the Joists

Installing deck boards perpendicular, or at 90°, to the joists is the most common and straightforward layout. It creates a traditional appearance, simplifies installation, and typically produces less waste than diagonal or more complex patterns. However, some extra material should be allowed for cuts, defects, and installation errors, so this calculator adds 10% to the estimate.

Deck Boards Installed 45° to the Joists

Installing deck boards at a 45° angle to the joists creates a diagonal pattern across the deck. Diagonal installation requires more cuts and produces more waste with each cut. This calculator adds 15% more material to account for that waste.

Complex Deck Board Patterns

Chevron, herringbone, inlays, and other intricate deck board patterns can create a distinctive appearance but generally require more cutting, blocking, and material. These layouts may also increase labor costs and can produce up to 20% waste. For unique pattern ideas, check out this article on Deck Patterns and Layout Options.

Best Deck Board Materials for Your Deck

Wood and composite are the most common decking materials. Pressure-treated lumber is typically the most affordable wood option and is widely available. Cedar is another popular choice, offering a more natural appearance and chemical-free resistance to decay, but it generally costs more than pressure-treated lumber. Both require periodic maintenance and can crack, splinter, or warp over time, and time and money spent on maintenance and refinishing will add to long-term costs.

Composite decking typically costs more upfront than wood but requires much less maintenance and resists fading, rot, splintering, and insect damage. Composite decking is available in a wide range of colors and finishes and can provide a long service life without the regular staining and sealing required by wood decking. PVC decking offers many of the same low-maintenance benefits and can be a good choice for homes susceptible to wildfires.

For your deck framing, pressure-treated lumber is the most common choice. Be sure all fasteners and connectors are approved for use with treated lumber as well as the decking material you choose.

What tools are required to build a deck?

• Hammer
• Marker and/or Pencil
• Tape Measure
• Framing Square
• Speed Square
• Levels (4 feet or longer)
• Hand Clamps
• Chalk Line
• String
• Stakes
• Digging Tools for Footings
• Drill/Driver and Bits
• Circular Saw
• Table Saw and Miter Saw (optional)
• Jigsaw

Common Mistakes When Calculating Deck Materials

• Using deck square footage alone: Two decks with the same square footage can require different quantities of decking depending on their dimensions, board lengths, and layout.
• Not considering available board lengths: Choosing board lengths that don't correspond well with deck dimensions can create unnecessary waste and increase material costs.
• Ignoring the waste factor: Allow extra decking for cuts, offcuts, defects and installation errors, particularly with angled or complex layouts. This calculator accounts for the waste factor.
• Using the wrong joist spacing: The type of decking you use and the span of your joists will determine their spacing. Joist spacing will also affect the amount of fasteners you will need.
• Treating nominal board width as actual width: A nominal 6-inch deck board is typically about 5.5 inches wide. This calculator uses nominal board width to approximate the combined width of the board and gap, and adds an extra board to the estimate.
• Forgetting to account for perimeter and dividing boards: Picture-frame and dividing boards can reduce the length of the field boards, and you may end up purchasing longer boards than you need if you don’t factor them in. Also, don’t forget to add these boards to your shopping list.
• Forgetting stairs: Include decking for stair treads and landings when calculating the total material quantity.

More Handy Design Tools

Along with this deck material estimator, the design tool and additional calculators below can help simplify your deck-planning process.

• Design Tool
• Cost to Build Your Deck
• Composite Cost Calculator
• Stairs Calculator
• Railing Calculator
• Baluster Spacing Calculator

Deck Design Inspiration

Explore the beautiful decks featured in these articles to find inspiration for your own deck design.

• Luxury Deck Features That Will Wow Your Guests
• Why Use a Cocktail Railing?
• How to Choose a Deck Railing Color
• 25 Best Deck Design Ideas