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Glulam Beam Deflection Checker

Check calculated glulam beam deflection against standard L/180 (roof) or L/360 (floor) code limits.

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
19.69 ft
Schematic, drawn to the proportions you entered — not to scale on screen.

Calculated deflection

0.6 in

High confidence

PASSES — calculated deflection (15.34 mm) is within the 16.67 mm allowable limit.

Allowable limit
0.66 in

With the figures above, the calculated deflection comes to 15.3 mm. Behind that figure, allowable limit is the biggest single quantity at 16.7 mm; start there if the total looks wrong. This is calculated for United States and cites IRC 2024. Building in another market? Change the selector above so the units and code reference follow.

Add the equipment this sizes

This result is a specification — 0.604 in — 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

  • Uniformly-loaded simple beam deflection: Δ = 5wL⁴/(384EI); standard code deflection limits are L/180 for roof beams and L/360 for floor beams

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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

Why does deflection depend on span to the fourth power?
The uniformly-loaded simple beam deflection formula, Δ = 5wL⁴/(384EI), has span (L) raised to the fourth power — so doubling the span increases deflection sixteen-fold for the same load and section, making span by far the most sensitive variable.
What's the difference between the L/180 and L/360 limits?
L/360 is the tighter, more common limit for floor beams (and any beam supporting a plaster or rigid ceiling below, which cracks under smaller movements); L/180 is a looser limit typically permitted for roof beams without a plaster ceiling underneath.
Does passing this deflection check mean the beam is structurally adequate overall?
No — this checks deflection (serviceability) only. The beam's bending stress and shear capacity must be checked separately against the applied loads to confirm overall structural adequacy.