🏡 Decking Calculator
Calculate boards, fasteners, and materials for your deck project.
Deck Boards Needed
How to Use This Calculator
Enter your deck length and width, choose your board width (5/4x6 is the most common pressure-treated choice at 5.5 inches actual), set the gap size, and pick your layout. The calculator gives you the total board count including waste, plus linear footage and fastener estimates.
Measure your deck length and width in feet. For an irregular shape, break it into rectangles and add them together.
Choose your board width. Standard 5/4x6 decking runs 5.5 inches wide. Composite boards are often 6 inches wide.
Set the gap. A 1/4-inch gap is standard for most lumber. For green or wet lumber, use 1/8 inch since the wood will expand as it dries.
Select diagonal if you want a 45-degree layout. This pattern adds roughly 15% to material costs because of the extra cuts at the perimeter.
Deck Board Formula
The layout factor is 1.0 for straight decking and 1.15 for diagonal. The waste factor covers splits, defects, and end cuts. Add 10% for straight layouts and 15% for diagonal.
Example Projects
Tips for Your Project
Buy all your boards from the same unit or bundle when possible. Color and grain variation between different lots of pressure-treated lumber can be noticeable. For a 16x20 ft deck, budget roughly 15-20% extra on your board count to account for crown sorting, splitting, and twisted boards you will reject at the store. Lay boards crown-up (bow facing up) so foot traffic pushes them flat over time rather than creating a tripping edge.
For composite decking, check whether the manufacturer requires hidden fasteners. Many composite systems use proprietary clip systems that add to your fastener count significantly. A 16x20 ft composite deck can require 400 or more hidden clips plus the track screws. Get the fastener spec sheet before you buy.
Frequently Asked Questions
How many deck boards do I need?
Deck area ÷ (board width + gap) × deck length gives board count. Add 10–15% waste. Our calculator handles this automatically.
What size deck boards are standard?
5/4 × 6 (5.5" wide), 2×6 (5.5" wide), 2×4 (3.5" wide). Lengths: 8, 10, 12, 16, 20 ft. Most common decking is 5/4×6 pressure treated.
What gap should I leave between deck boards?
1/8" to 1/4" gap for drainage and expansion. For green/wet lumber, use smaller gaps as wood expands when it dries.
How far apart should deck joists be?
12" or 16" on center for 5/4 decking. 16" or 24" for 2× lumber. Closer spacing for diagonal decking.
What is composite decking?
Composite decking is made from a blend of wood fiber and plastic. It requires less maintenance than wood, won't rot, and resists insects and mold.