Deck & Floor Joist Span Chart (IRC Table Guide)
Understand maximum clear spans for 2x6, 2x8, 2x10, and 2x12 joists according to International Residential Code (IRC) structural tables.
1. Understanding Lumber Joist Span Variables
Joist span capacity depends on four structural factors: Lumber Depth (2x6 through 2x12), Wood Species & Grade (#2 Southern Pine / Douglas Fir), Joist Spacing (12", 16", or 24" OC), and Design Load (40 psf live load + 10 psf dead load).
| Board Size | 12" On Center | 16" On Center (Std) | 24" On Center |
|---|---|---|---|
| 2x6 Lumber | 10 Ft 9 In | 9 Ft 9 In | 8 Ft 0 In |
| 2x8 Lumber | 14 Ft 2 In | 12 Ft 7 In | 10 Ft 3 In |
| 2x10 Lumber | 18 Ft 0 In | 16 Ft 1 In | 13 Ft 2 In |
| 2x12 Lumber | 21 Ft 10 In | 19 Ft 6 In | 15 Ft 11 In |
Calculate Your Joist Clear Span
Select your lumber size, spacing, and wood species to view instant IRC maximum span tables.
Launch Joist Span CalculatorFrequently Asked Questions
How far can a 2x10 joist span for a residential floor?
A Southern Pine #2 grade 2x10 joist spaced 16 inches on center can safely span up to 16 feet 1 inch under standard 40 lbs/sq ft live load conditions.
What is L/360 deflection in structural joist tables?
L/360 means the maximum allowable sag under full design load is the span length divided by 360. For a 12-foot span (144 inches), maximum deflection cannot exceed 0.40 inches.