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Timber Beam Bending Stress Calculator

Calculate actual bending stress in a rectangular timber beam from applied moment and section dimensions.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-26 · v1.0.0

Market
Imperial · sales tax

Actual bending stress

10 MPa

High confidence

For the dimensions entered, expect a actual bending stress of 10 MPa. Set for United States against IRC 2024. The market selector changes both the units and the code cited.

Add the equipment this sizes

This result is a specification — 10 MPa — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • Rectangular section bending stress: fb = 6M/(b×d²), the standard flexure formula (fb = Mc/I) applied to a rectangular cross-section

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Frequently asked questions

What formula does this calculator use?
It uses fb = Mc/I applied to a rectangular cross-section, which simplifies to fb = 6M/(b×d²) — the standard flexure formula for a rectangular timber beam.
Why does beam depth matter more than beam width for reducing stress?
Depth is squared in the denominator (b×d²), so doubling a beam's depth cuts bending stress to roughly a quarter of its original value, while doubling width only halves it — depth is the far more efficient dimension to increase.
How do I know if this stress is acceptable?
This calculator gives the actual (demand) bending stress from your applied moment — compare it against your wood species and grade's allowable bending stress Fb (adjusted for load duration and other NDS factors) to confirm the beam is adequate.