How to Calculate Floor Joists
Number of joists: (Floor length x 12 / Spacing) + 1
Board feet: Joists x Span x (nominal width x nominal depth / 12)
Deflection: 5wL^4 / (384EI) - must be less than L/360
Maximum Joist Spans (SPF #2, 40 psf live)
- 2x6 @ 16" OC: 9 ft 1 in
- 2x8 @ 16" OC: 12 ft 0 in
- 2x10 @ 16" OC: 15 ft 4 in
- 2x12 @ 16" OC: 18 ft 8 in