Deck Joist Calculator
Calculate the number of joists required for your deck. Understand how joist spacing, size, and wood type affect your deck’s structure.
Step 1: Deck Dimensions
Understanding Deck Dimensions
The length and width of your deck determine how many joists you’ll need. Standard residential decks typically range from 10×12 feet to 20×20 feet. Always add 10% extra for waste and mistakes.
Step 2: Joist Specifications
About Joist Spacing
Standard joist spacing is 16 inches on center (OC). For composite decking, 12-inch spacing is recommended. For heavy loads or diagonal decking, consider 12-inch spacing for extra strength.
Deck Joist Calculation Results
Total Joists Required
Joist Spacing Comparison
| Spacing | Joists Needed | Strength Rating | Material Cost | Recommended For |
|---|
Material Cost Breakdown
Joist Calculation Formula
Number of Joists = (Deck Width × 12) / Joist Spacing + 1
The number of joists is calculated by converting deck width to inches, dividing by joist spacing in inches, then adding one for the end joist. Always round up to the nearest whole number.
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