Deck Calculator: How Much Decking Do I Need?

Dreaming of a new deck? Before you start envisioning your future BBQs and backyard parties, there are a few logistics to sort out, including how much decking you need. With a few measurements and this deck calculator, you can easily figure out the right amount of decking to order.

How Much Decking Do You Need for Your Deck?

The amount of decking you need depends on the total square footage of your deck and the size of your deck boards. We also recommend purchasing 10% more material than you need to account for wastage, cutting, and potential mistakes. 

We’ll dive deeper into those factors shortly, but here’s a glance at the number of 5.5-inch-thick, 12-foot-long deck boards you’d need for different-sized decks: 

Calculating the Right Amount of Decking

If you know the size of your deck and the dimensions of the deck boards, plug them into this formula to determine how much decking you need:

Number of Deck Boards Needed = (Total Deck Square Footage / Individual Deck Board Square Footage) x 1.1

As an example, let’s say you’re building a 12-by-12-foot deck and want to use 5.5-inch-thick deck boards. Here’s how to calculate how much decking you need:

1. Divide the deck board’s width by 12 to convert it from inches to feet. A 5.5-inch board is 0.46 feet.

2. Find the square footage of one deck board by multiplying the length and width. For a 5.5-inch board that’s 16 feet long, that’s 5.52 square feet.

3. Divide the deck’s square footage (144) by a deck board’s square footage (5.52) to get 26.09.

4. To account for 10% overage, multiply that by 1.1. This gives you 28.7.

5. Since you can’t buy 0.7 of a deck board, round up to 29 boards.

How to Measure Your Deck for Decking

You’ll need to get your deck’s measurements before buying decking. Here’s how to do that, depending on your circumstances:

• If you’re replacing an existing deck, measure the current length and width of the deck. Then, multiply them to find the square footage.

• If you’re building a new deck, you’ll decide on your deck’s dimensions during the planning process. 

Who to Hire to Install Decking

Planning a deck is a big undertaking, and calculating how much decking you need is just one part of the job. Before you can break ground on your new deck, you’ll also have to map out the deck’s layout, choose a decking material, check your local building codes and HOA regulations, and obtain permits.

With that said, there are advantages to designing and building your own deck. By going it alone, you’ll save $15 to $35 per square foot in labor. For a 16-by-20-foot deck, that’s $4,800 to $11,200.

While those savings might sound tempting, this type of work is best left to those with carpentry skills and an understanding of deck-building codes. If that’s not you, your best bet is to hire a decking contractor who can ensure that your deck is safe, sturdy, and legally compliant.