Does this calculator replace a structural engineer?

No. It is a planning and pre-check tool for estimating whether a beam size is in the right range for a given span and load, not an approved structural calculation. For any load-bearing beam, have the final size, span and load confirmed by a licensed structural engineer and checked against your local building code before you build.

Which design standards does this calculator actually compute?

Only the US NDS 2018 method (National Design Specification, AWC) is fully computed today, covering deflection, bending and shear. Eurocode 5 and AS 1720 are selectable as your project's applicable standard, but this build does not yet have real span-check data for them -- always verify against your official local design standard.

Does this replace certification for a building permit in Australia?

No. Most Australian councils require a certified engineer's calculation under AS 1720 for any load-bearing beam before permit approval. Use this calculator for planning only, and confirm the final size with a structural engineer.

Wood Beam Span Calculator — AS 1720 (Australia)

Wood Beam Span Calculator: Deflection, Bending and Shear Check

This calculator checks whether a wood beam of a given size, species and grade can safely carry a chosen load over a chosen span, testing deflection, bending stress and shear stress in one pass. Enter the beam's width, depth, species/grade, span, load and deflection limit, and get a pass/fail on all three. It is a planning and pre-check tool, not a substitute for a structural engineer or your local building code -- beam sizing is safety-critical, and a fully computed result is currently only available under the US NDS 2018 design standard.

How to Use the Wood Beam Span Calculator

Select the design standard for your project -- US NDS 2018 is the only standard this calculator fully computes today; Eurocode 5 and AS 1720 are selectable but not yet populated with real results.
Choose a nominal beam size (2x8 through 4x12) or enter a custom width and depth in inches.
Pick a species/grade preset (Douglas Fir-Larch, Hem-Fir, Spruce-Pine-Fir or Southern Pine) or enter custom design values.
Enter the span, the uniform load per linear foot, and a deflection limit -- L/360 is the standard default for beams.
Read the pass/fail result for deflection, bending stress and shear stress.

The Math Behind the Check

Three checks run together: bending stress (fb = M/S, with M = wL^2/8 for a simply supported beam) against the adjusted bending design value; shear stress (fv = wL/(2bd)) against the adjusted shear value; and deflection (5wL^4/384EI) against your chosen limit (L/360 is standard).

Whether a beam passes depends entirely on its cross-section, species/grade, span, load and deflection limit -- there is no single "maximum span" that applies universally. This calculator computes a real result from your inputs under the US NDS 2018 method only; other design standards remain selectable placeholders until real span data is sourced for them.

Australian Design Standard

Timber beam spans in Australia are designed to AS 1720 (Timber Structures) -- this calculator's Span mode currently computes real results only using the US NDS 2018 method, so AS 1720 is selectable as your project's standard but not yet populated with Australian span data.

Tips and Common Mistakes

Having a structural engineer review and certify a single beam span check typically costs around AUD 350-1,300 in Australia, depending on complexity.

Adjustment factors (load duration, wet service, temperature, and others) default to 1.0 -- only change them if you know your project's conditions genuinely differ from standard dry, normal-duration assumptions.
This is a planning aid, not a stamped structural calculation. For any load-bearing beam, confirm your final size, span and load against your applicable design standard or a licensed structural engineer before you build.