Understanding U.S. Wood Beam Loads
A wood beam carries weight across an open span. In U.S. projects, that weight is usually stated in pounds and feet. The load may come from floors, roofs, decks, snow, storage, or people. A good first check compares bending, shear, and deflection. Each check protects a different failure mode. Bending checks the tension and compression in the beam. Shear checks sliding force near supports. Deflection checks visible sag and service comfort.
Important Inputs
The span is the clear distance between supports. Width and depth define the beam section. Depth strongly changes strength because section modulus uses depth squared. Stiffness changes even faster because moment of inertia uses depth cubed. The calculator also asks for Fb, Fv, and E. These values describe bending strength, shear strength, and stiffness. They vary by species, grade, moisture, duration, and use. Adjustment factors let you model common design changes.
How Results Should Be Read
The result shows demand values and adjusted allowable values. A ratio below 100 percent means that check passes for the entered assumptions. A ratio above 100 percent means the beam is over the selected limit. The controlling check is the highest ratio. Sometimes a beam has enough strength but fails deflection. This is common on long spans. A deeper beam often improves both bending and sag.
Practical Planning Notes
Use realistic loads before trusting a result. Floor loads often include dead load and live load. Roof loads may include snow and construction weight. Deck beams may need concentrated loads from posts. This tool uses simplified beam formulas. It does not replace engineering design. It does not check bearing length, lateral bracing, notches, holes, fasteners, seismic loads, or local code rules.
When To Get Help
Use the calculator for early sizing and comparison. Save the report for discussion. A licensed engineer or qualified building professional should verify final members. This is especially important for homes, decks, garages, roofs, and public spaces. Exact species, grade stamp, load path, and support conditions matter. Small changes can alter the safe load by a large amount.
Record every assumption before ordering lumber. Recheck spans after layout changes. Use conservative values when loads are uncertain. Review local permits before starting work too.