Wood Beam Span Calculator

in
Actual dimension. 2×10 = 9.25 in actual.
in
lbs/ft
Total uniform load per linear foot of beam.
psi
Douglas Fir-Larch #2: ~900 psi; LVL: ~2600 psi.
Construction

Estimate the maximum safe span for a wood beam based on size, species, and load.

Formula

L_max = √(8 × Fb × S / w); S = b×d² / 6
  • This is a simplified allowable stress calculation — for actual design, use a licensed structural engineer.
  • S = section modulus; Fb = allowable bending stress; w = uniform load (lbs/in).
  • Add L/360 deflection check for floor beams.

2×10 beam, 300 lbs/ft load, Fb=1200

Inputs
  • Beam Depth (d): 9.25 in
  • Beam Width (b): 1.5 in
  • Distributed Load (w): 300 lbs/ft
  • Allowable Bending Stress (Fb): 1200 psi

S = 1.5×9.25²/6 = 21.4 in³. Mallow = 1200×21.4 = 25,656 in-lbs. L = √(8×25,656/25) = 90.7 in = 7.6 ft.

Frequently asked questions

Should I use this for structural design?
No — consult a licensed structural engineer for any load-bearing beam. This is for estimation only.