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Related Reading

Formwork plywood grades across EN, APA and ANSIThe cross-reference guide explains how the APA span system relates to the EN and ANSI grading frameworks.
Plywood standard sizes and dimensionsCovers the nominal-versus-actual thickness gap that affects how a span rating maps to the panel you measure.
Properties of plywoodThe parent properties guide covers the strength and stiffness that determine a panel's span rating.
Film-faced plywoodVinawood's EN 636 film-faced formwork range, rated by service class and reuse rather than by APA span.

Quick Answers

What is a span rating for plywood?
It is the maximum recommended center-to-center spacing of supports, in inches, that a panel is rated to span. A two-number rating like 32/16 gives the roof spacing (32 inches across rafters) and the subfloor spacing (16 inches across joists). The rating is printed on the APA grade stamp and reflects the panel's tested performance, not just its thickness.
Can 1/2 inch plywood span 24 inches?
Not for a floor. A typical 1/2-inch panel carries a 32/16 rating, meaning a 16-inch subfloor limit and a 32-inch roof limit. So 1/2-inch plywood can span 24 inches as roof sheathing (within its 32-inch roof rating) but not as subflooring, where 16 inches is the limit. Always read the panel's own stamp rather than assuming from thickness.
How far can 3/4 inch plywood span?
A 3/4-inch (23/32") panel commonly carries a 48/24 rating: up to 48 inches as roof sheathing and up to 24 inches as subfloor. As a Sturd-I-Floor single-layer panel it is typically rated 24 o.c., suiting joists up to 24 inches apart. The exact limit is whatever the stamp reports for that specific panel.
When should I use 1/2 vs 3/4 inch plywood?
Match the panel to the support spacing and the load. A 1/2-inch (32/16) panel suits roof sheathing and 16-inch-joist subfloors. A 3/4-inch (48/24) panel suits wider 24-inch joist spacing, single-layer floors, and heavier loads such as tile substrates. When joists are 24 inches on center or the floor carries heavy loads, step up to 3/4 inch.