Deck Calculator
Estimate the materials needed for your decking and joists.
Framing & Decking
Your Estimated Materials
Deck Boards Needed
0
Joists Needed
0
This is an estimate for informational purposes. Always consult a professional for building plans.
About the Deck Calculator
Building a deck is a major project, and ordering the right amount of material is the first step to success. This calculator helps you accurately estimate the number of deck boards and support joists you'll need based on your deck's dimensions and your chosen spacing. Plan your project with confidence and avoid unnecessary trips to the lumber yard.
Formula Explained
The calculator uses standard construction formulas to estimate your material needs:
- Joists Calculation: It determines the number of joists needed to frame your deck. The formula is `(Deck Length / Joist Spacing) + 1`, rounded up.
- Deck Boards Calculation: It calculates the total number of boards needed to cover the surface of the deck. The formula is `(Deck Width / (Actual Board Width + Gap))`. The length of each board is assumed to match the length of your deck.
How to Build a Better Deck
A well-built deck is safe, durable, and beautiful. Here are some tips for a professional result:
Check for Square
Before installing joists, ensure your frame is perfectly square using the 3-4-5 method to check the corners.
Consistent Gapping
Use a spacer (like a nail or a small block of wood) between deck boards to ensure a consistent 1/8" or 1/4" gap for water drainage.
Use Quality Fasteners
Invest in high-quality, corrosion-resistant deck screws or hidden fasteners. They will last longer and prevent rust stains.
Seal or Stain Your Deck
Protect your investment by applying a quality sealer or stain to your wood deck. This will prevent water damage and rot, extending its life.
Frequently Asked Questions
How many deck boards do I need? →
To calculate the number of deck boards, you need to know the total area of your deck and the width of a single board (including the gap between boards). The formula is: (Deck Length × Deck Width) / (Board Width + Gap Width). Our calculator performs this calculation for you based on your inputs.
What is the standard spacing for deck joists? →
The standard spacing for deck joists is typically 16 inches on-center. This provides a strong and stable frame for most decking materials. For some composite decking or if you plan to lay boards at a 45-degree angle, a closer spacing of 12 inches on-center is often recommended.
What is the actual width of a 5.5-inch deck board? →
A standard '5/4 x 6' deck board, which is the most common size, has an actual width of 5.5 inches. Lumber dimensions are often 'nominal,' meaning the name is based on the rough-sawn size before the wood is planed and smoothed. Always use the actual width for your calculations.
How do you calculate the number of joists needed? →
To calculate the number of joists, divide the length of your deck by the joist spacing (e.g., 16 inches), and then add one extra joist for the end. The formula is: (Deck Length in inches / Joist Spacing in inches) + 1. The result should be rounded up to the nearest whole number.
Should deck boards be installed perpendicular or parallel to the house? →
Deck boards should almost always be installed perpendicular to the joists for proper support. If your joists run away from the house, your deck boards should run parallel to the house. This ensures each board is supported by multiple joists.