Deck Material Calculator

Imagine you're building a cozy 12x16 foot backyard deck using standard pressure-treated pine. Your boards are 5.5 inches wide, and you're leaving a 1/4-inch (0.25 in) gap between them. First, we convert the board width and gap to feet: (5.5 + 0.25) / 12 = 0.479 feet. Now, we divide our 12-foot deck width by this number: 12 / 0.479 = 25.04 rows. Since we can't buy a fraction of a board, we round up to 26 rows. Since each row runs the full 16-foot length of the deck, you'll need 26 boards that are 16 feet long. We highly recommend adding a 10% waste buffer, so you should grab 29 boards at the store just to be safe!

Let's say you're upgrading to a gorgeous, low-maintenance 20x24 foot composite deck. Composite boards don't expand as much as natural wood, so we'll use a tighter 1/8-inch (0.125 in) gap. If we lay the boards along the 24-foot side, we need to span the 20-foot width. Let's calculate the rows: 20 feet divided by (5.5 + 0.125 inches converted to feet) gives us 20 / 0.46875 = 42.67 rows, which we round up to 43 rows. Each row is 24 feet long. If you buy 24-foot boards, you'd need 43 of them. But since 20-foot boards are easier to transport, you might buy those instead. 43 rows times 24 feet is 1,032 total linear feet. Dividing this by 20-foot boards gives us about 52 boards. Adding a 15% waste factor for composite cuts means you should order 60 boards total.

For a sweet and simple 10x10 foot cedar deck, the math is incredibly satisfying because the dimensions are perfectly square! We are using beautiful natural cedar 2x6 boards (which actually measure 5.5 inches wide) and leaving a standard 1/4-inch gap. To find the rows: 10 feet (or 120 inches) divided by 5.75 inches (board width + gap) equals 20.86 rows. Rounding up, we get 21 rows. Because your deck is exactly 10 feet long, you can buy 21 boards that are 10 feet long with absolutely zero cutting required! Add 2 extra boards (about 10% waste) to cover any natural wood knots or blemishes, making it 23 boards total.

A 'picture frame' border is a stunning design where boards run around the outer edge of your deck to hide the raw cut ends of the main floorboards. If you're building a 14x18 foot deck with a double-board border, you'll need to calculate both the outer frame and the inner field. The outer border wraps around the perimeter, requiring mitered 45-degree corner cuts. Because of these complex angles, you'll want to budget a 20% waste factor. After calculating the linear footage for the border and the remaining interior rows, you'll need about 55 boards at 16 feet long to complete this gorgeous, high-end look.

Diagonal Decking

If you want to give your deck a high-end, custom look by laying your boards at a 45-degree angle, you'll need to adjust your math. Diagonal decking looks stunning, but it requires a lot more angled cuts at the ends of the boards, which increases your waste factor to about 15%. Plus, you'll need to place your underlying joists closer together (usually 12 inches instead of 16 inches) to make sure the diagonal spans are fully supported and don't sag.

Multi-Level Decks

Building a deck with multiple steps or levels is a fantastic way to zone your backyard, but it means you can't just use a single flat-area calculation. You'll need to break your deck down into separate sections and calculate the boards for each level individually. Don't forget to account for the stairs, too! Stair treads and risers require extra thick boards and careful measuring to ensure they are safe and comfortable to climb.

Picture Frame Borders

A picture frame border is when you run a border of boards perpendicular to the main decking around the outside edge. It hides the raw, cut ends of your boards and looks incredibly polished. If you go this route, you'll need to calculate the linear footage of the border separately, miter the corners at a 45-degree angle, and install extra framing underneath to support the border boards. We recommend adding a 15-20% waste buffer for this style due to the precise cuts involved.