Load Bearing Span

Calculate the maximum allowable span for dimensional lumber floor joists based on IBC Table 2308.4.1.1. Assumes 40 psf live load and 10 psf dead load (L/360 deflection).

Wood Species & Grade

Joist Spacing (O.C.)

Max Allowable Spans

2x8 Joist

2x10 Joist

2x12 Joist

Douglas Fir-Larch #2 (16" O.C.) Default Values:

2x8: 12' 6"
2x10: 15' 2"
2x12: 17' 7"

How It Works

Spans are calculated based on Modulus of Elasticity (E) and Bending Design Value (Fb). When joist spacing increases, the load per linear foot on each joist increases, exponentially reducing the maximum span.

Never notch the middle third of a joist span, as bending stresses are highest there (IBC 2308.4.2.4).