Floor Joist Calculator
Calculate joist span, spacing, and costs for your construction project
Disclaimer: This calculator provides estimates only. Always consult with a structural engineer or local building codes for official requirements. Results are not guaranteed and ClayDesk assumes no liability for construction decisions made based on these calculations.
Floor Joist Calculation Formula
Number of Joists = (Room Width × 12) / Joist Spacing + 1
This formula calculates how many joists are needed based on room width and spacing between joists.
Why Floor Joist Calculations Matter:
Proper joist calculation is essential for:
- Structural integrity and safety of floors
- Preventing saggy or bouncy floors
- Meeting building code requirements
- Optimizing material costs for construction projects
- Planning deck, loft conversion, and floor truss projects
Key Insights:
Smaller Spacing
12" OC provides stronger floors but requires more joists and higher material costs
Larger Joists
2×12 joists can span longer distances but cost more per linear foot