Building a deck is a rewarding DIY project that can create a fantastic outdoor living space. A crucial step in the planning phase is figuring out exactly how many deck boards you'll need. Ordering the wrong amount can lead to project delays or unnecessary costs. Our Decking Calculator is a simple tool designed to help you accurately estimate the number of boards required to cover your deck's surface. By accounting for the width of your deck, the width of your boards, and the essential gap between them, this calculator ensures you can buy your materials with confidence.
How to Use the Decking Calculator
Estimating the number of deck boards you need is a quick process:
- Select Units: Choose whether you are working with imperial (inches) or metric (millimeters) measurements.
- Enter Deck Width: Input the total width of your deck—this is the dimension your deck boards will be spanning across.
- Enter Board Width: Input the actual width of a single deck board. A standard 5/4" x 6" board is actually 5.5 inches wide.
- Enter Gap Width: Specify the size of the gap you plan to leave between each board for drainage. A 1/8 inch (or 3-4 mm) gap is typical.
- Calculate Boards Needed: Click the "Calculate" button to see the total number of deck boards required to cover the width of your deck.
The Math Behind the Calculation
The calculation is a straightforward process of figuring out how many "board-plus-gap" units fit across the total width of your deck.
The "Effective Width" of a Deck Board
You can't simply divide the deck width by the board width. You must also account for the small gap left between each board, which is essential for allowing water to drain through and for the wood to expand and contract with changes in humidity.
The "effective width" of each board is its actual width plus the width of one gap.
Effective Width = Board Width + Gap Width
The total number of boards needed is then found by dividing the total width of the deck by this effective width. Since you can't buy a fraction of a board, the calculator automatically rounds the result up to the next whole number.
Boards Needed = Deck Width / Effective Width
Important Project Planning Considerations
Board Length and Layout
This calculator tells you how many *rows* of boards you'll need. The number of physical boards you need to buy will also depend on the length of your deck and the length of the boards you purchase (e.g., 8-foot, 12-foot, or 16-foot boards).
If the length of your deck is longer than the boards you buy, you will need to join boards end-to-end. It's best practice to stagger these joints across different rows so they don't all line up, which creates a stronger and more visually appealing deck surface. Be sure to account for this in your total material purchase.
Choosing Your Decking Material
- Pressure-Treated (PT) Lumber: This is the most common and affordable option. It's pine or fir that has been chemically treated to resist rot and insects.
- Cedar or Redwood: These woods are naturally resistant to rot and insects, offering a beautiful, natural look without the chemicals of PT lumber, but at a higher cost.
- Composite Decking: Made from a mix of wood fibers and recycled plastics, composite decking is a low-maintenance, highly durable option that won't rot, splinter, or warp. It has a higher upfront cost but requires no annual staining or sealing.
Don't Forget the Framing and Hardware
This calculator is only for the surface decking boards. A complete deck project also requires a sturdy substructure (joists, beams, and posts) and the right hardware (deck screws, joist hangers, and concrete footings). Always ensure your deck's framing is built to local building codes for safety and stability.
Frequently Asked Questions
Why is a gap between deck boards necessary?
The gap is crucial for two reasons. First, it allows rainwater to drain through the deck instead of pooling on the surface, which prevents rot and water damage. Second, wood naturally expands and contracts with changes in moisture and temperature. The gap gives the boards room to swell without buckling against each other.
What is the actual width of a 5/4" x 6" deck board?
Lumber dimensions can be confusing. A board marketed as "5/4 x 6" (five-quarter by six) has a nominal thickness of 1.25 inches and a nominal width of 6 inches. However, after milling and surfacing, its actual dimensions are closer to 1 inch thick and 5.5 inches wide. You should always use the actual width (5.5 inches) in your calculations for an accurate result.
Does this calculator include a waste factor?
No, this calculator gives you the exact number of rows needed. It's highly recommended that you add a waste factor of 10-15% to your total board purchase to account for cuts, mistakes, and any damaged boards.