Lumber Span Calculator
Estimate maximum allowable spans for floor joists and rafters based on species, grade, size, and spacing.
Lumber Span Calculator
Estimate maximum allowable spans for floor joists and rafters based on species, grade, size, and spacing. Values are from IRC span tables — always verify with your local building department.
Maximum Allowable Span
Design value details
Fb (Bending): — psi
E (Modulus of Elasticity): — × 10⁶ psi
Actual depth: — in
Span calculated using IRC simplified method: L/360 deflection limit and Fb bending stress limit. Dead load = 10 psf assumed.
⚠ Important: These values are estimates for reference only. Actual spans depend on specific conditions including load duration, moisture, temperature, bearing conditions, and local code amendments. Always consult IRC span tables and your local building official for final determination.
Select application type, species group, grade, nominal size, and spacing. The calculator estimates maximum span using IRC simplified bending and deflection formulas.
Related Materials
Laminated veneer lumber (LVL) is a high-strength engineered wood product made from thin wood veneers bonded with structural adhesive under heat and pressure. It is the most commonly specified engineered beam and header material in residential and light commercial construction.
I-joists are engineered wood floor and roof framing members with an I-shaped cross section — LVL or solid lumber flanges bonded to an OSB or plywood web. They are the dominant floor framing material in new residential construction, offering long spans, dimensional stability, and lightweight handling.