How Many Deck Boards Do I Need?

If you’re planning to build or resurface a deck, one of the questions you will need to answer is: "How many deck boards do I need?" 

Determining the number of deck boards helps inform the cost for your project. Having this number in mind before you start building is essential — nobody wants to blow their budget. That said, the number of deck boards needed for your project can vary for a variety of reasons, including the type of decking material you choose, the size of your deck and more.

Follow along to learn how to calculate the number of deck boards you need for your next decking project.

Steps to Calculate Deck Boards Needed

Let's get started with these eight easy steps.

Step 1: Select the Shape of the Deck

Not all decks are squares or rectangles. Your deck can be pentagonal, hexagonal, or even octagonal; really, your shape options are virtually limitless as long as it fits within your available space. Take a look at our free deck plans to see some of our most popular deck shapes. 

Can’t find one you’re in love with? You can customize each of our deck plans or start from scratch with our Deck Designer tool.

Step 2: Determine the Square Footage of the Deck

Once you choose your design, calculate the overall length and width. To do this, grab a buddy and use a 25-foot tape measure to give substance to your vision. Be sure to take into account any extra angles, nooks, crannies and staircases in your calculations. Take detailed notes, and even make a design sketch, if you haven’t already, to see how your measurements will pan out.

Step 3: Figure Out the Square Footage of Each Board

After calculating your square footage, you'll need to select deck boards with widths that fit inside your design's parameters. Luckily, Trex composite deck boards offer a range of quality options and are manufactured in three widths:

• The 1” Transcend® and Enhance® boards are .94” x 5.5”
• The 1” Select® boards are .82” x 5.5”
• Transcend and Select boards also are available in a 2x6 dimension, or 1.3” x 5.5”

Step 4: Determine the Length of Each Board

The lengths of the decking boards usually range from 8’ to 20’. Trex boards come in 12’, 16’ and 20’ lengths. You’ll also need to know the length of each board to calculate the overall size of your deck.

Especially with uniquely shaped decks, you'll need a saw to cut composite deck boards as you assemble your deck properly. Not every board will fit perfectly at their full length — some boards will need to be cut at an angle to make them fit together correctly. You may end up with extra boards, due to waste created by cutting them to the right angles and lengths. Consider holding onto these boards to reduce costs in case you need to replace boards or expand your deck later on.

Step 5: Calculate the Number of Deck Boards

To that end, anticipate having waste on your decking project. The general rule of thumb is that you need 5% extra decking material to account for waste and mistakes. For example, if your project calls for 80 boards for 800 square feet, add another 40 square feet for waste, or four extra boards.

To determine the number of deck boards you need to build your deck:

• Take the area of your deck (as shown in Step 1) and divide that number by the board area (Step 3)
• Deck Depth (in inches) / Board Width (inches) = Number of deck boards needed
• 0.05 x Number of deck boards needed = Total number of extra deck boards you should purchase
• Total number of deck boards needed + Total number of extra deck boards = number of boards you should order

Let’s work through an example. Imagine we want to build a 20’x12’ deck using a deck board that is 5.5 inches wide and 20” in length.

• First, calculate the depth in inches: 12x12 = 144 inches 
• Next, divide the board depth (in inches) by the board width (For most 1x6 or 2x6 boards, the width is 5.5”): 144/5.5= 26.18
• Then, round up to get a whole number: 27 boards
• Next, multiply the total number of deck boards needed by 0.05 to account for the additional 5% of material needed for waste. Again, round up to get a whole number: 0.05 x 27 = 2 extra boards
• Lastly, add the waste boards to the total. 27 + 2 = 29 boards total

Your actual results will vary depending on the size and shape of your deck.

Step 6: Use a Specialized Deck Cost Calculator

If those calculations seem a bit too much, skip the whole manual process. Use our Trex Cost Calculator to determine an estimated material cost for your project. The easy-to-use calculator factors in additional materials like a wood substructure and deck railing.

What to Watch Out for When Calculating the Number of Deck Boards for Your Deck

A deck is a big investment, but one you can enjoy for a lifetime. Rather than skimp when you’re in the planning phase, how about dreaming big? What do you really want out of your deck? Here are a few items to consider when planning your dream outdoor space.

Non-Standard Deck Shapes

Remember, you can make your deck any size or shape based on your needs and budget. Your shape and space requirements will impact how you use the deck board calculator. For example, a simple square or rectangular deck requires a fairly straightforward calculation, while non-standard designs might require more small calculations to determine overall measurements — but they’re not insurmountable.

If dreaming big is part of the plan, the cost calculator can handle it. You can easily design a deck that meets your needs while letting your guests spread out and enjoy themselves. Rather than cram your grill into the seating area, design a rectangular or hexagonal space off to one side of your deck to serve as the cooking area. That way, no one is trying to move around you as you prepare meals.

Double Decking

Perhaps you want a multi-level deck. You'll need to calculate the deck boards for two levels rather than one. Calculate each level separately. Keep in mind the extra supports you need to account for so your multi-level deck is stable and well built.

Also, remember to add safety measures and railings as required by code.

Joists, Support Beams, and Stairs

When looking to price out the more advanced pieces of your decking project, like the substructure and stairs, we recommend using our Trex Deck Designer tool. This tool accounts for the joists and support beams that hold everything together. It can also indicate how many fasteners and joist hardware pieces to purchase to ensure a smooth build. 

Stairs can be tricky to price out because local codes may differ on the width and spacing of the stairs. If you want to make your deck easier to access for guests who might have mobility issues, consider adding an ADA-compliant handrail system or ramp. 

Keep in mind, more complex designs like multi-level decks, ramps and stairs will require more framing materials and greatly impact the price of your deck.

How Many Deck Boards Do I Need for a 12’x12’ Deck?

A 12’x12’ deck is a typical size for a modest backyard structure. How many decking boards you need for a deck this size will vary depending on the Trex decking line you choose. We have calculated the number of deck boards needed for some of the most common deck board lengths.

For 2x6s, you'll need:

• 27 12-foot boards
• 21 16-foot boards
• 17 20-foot boards

These figures take into account waste from cutting the boards to their proper lengths. Now that you know the number of boards, you can contact your local Trex retailer to purchase the deck boards you need. Prices may vary based on your location as well as supply and demand.

Learn More About the Cost of Deck Boards

Now that you have an idea of how to calculate the number of deck boards you need for your build, you can jumpstart your deck construction project with our handy deck designer and decking calculator tools. Feel free to review our deck how-to articles for some inspiration as you make your dream backyard paradise a reality.