Wood Beam Calculator

Preliminary Planning for Wood Structures

This tool offers a basic estimation for the required size of a wood beam or joist based on its span and the load it needs to support. It's helpful for initial planning in DIY or construction projects. Disclaimer: This is for educational and preliminary estimation only. A qualified structural engineer must verify all final designs.

The Formulas Explained

The calculation is based on principles of structural mechanics:

• Maximum Bending Moment (M): For a uniformly loaded beam, M = (w * L²) / 8, where w is the load and L is the span.
• Required Section Modulus (S): S = M / F_b, where F_b is the allowable bending stress of the wood species. The calculator uses these principles to suggest a generic dimensional lumber size.

How to Use the Calculator

1. Beam Span (ft): Enter the length of the beam between supports in feet.
2. Load on Beam (lbs/ft): Enter the uniform load applied to the beam in pounds per linear foot.
3. Calculate: The tool will suggest a potential nominal wood beam size.

Real-World Example

A wood joist for a floor needs to span 14 feet and support a load of 50 lbs/ft (including the weight of the flooring and expected live load).

• Max Bending Moment (M): (50 * 14²) / 8 = 1225 lb-ft.
• The calculator would use this moment to determine a required section modulus and suggest a suitable beam size, such as a 2x8 or 2x10.

Frequently Asked Questions (FAQ)

• What does a size like '2x10' mean? This is the nominal dimension in inches. The actual 'dressed' dimension of a 2x10 is closer to 1.5 inches by 9.25 inches.
• Does this calculator account for wood species? No. This is a key simplification. The strength of wood varies greatly by species (e.g., Southern Pine vs. Douglas Fir). A professional design will specify the required species and grade of lumber.
• What about deflection? Like the steel beam calculator, this tool does not check for deflection (how much the beam bends). For floor and roof joists, deflection limits set by building codes are often the deciding factor in beam size, not just strength.