Joist Mid-Span Deflection

Formula and source

Mid-span deflection Δ = 5 × w × L⁴ / (384 × E × I) for uniformly loaded simple span. E and I from AWC NDS-2018 design values keyed to species / grade / size.

AWC NDS-2018 (National Design Specification for Wood Construction). IRC 2021 (International Residential Code). §R301.7.

Audience

This tile is built for carpentry and the adjacent professions in the Carpentry and Construction group. The interactive calculator runs entirely in your browser. No account, no fee, no advertising, no tracking.

Related tools

• Lumber Spans
• Beam Loading
• Plywood and OSB Sheathing Span Rating

Posture

Rough Logic answers the math question the working professional asks on the job. The site is a calm, fast, ad-free, account-free, ever-free reference. It does not interpret code. It does not replace the licensed professional. It does not store your inputs. The Authority Having Jurisdiction governs all installations and inspections.