Glossary
Deflection
Also called: sag, pallet sag, deflection limit
Reviewed
Deflection is how far a pallet bends or sags under load, measured at the point of greatest movement. Common limits are about 1.9 to 2% of the span in rack storage (roughly 0.75 in on a 44 in span), 1.5 to 2% on the floor, and 0.5 in or less for automated warehouses and AS/RS.
Typical deflection limits
| Situation | Typical limit |
|---|---|
| Rack storage | about 1.9 to 2% of the span (about 0.75 in at 44 in) |
| Floor support | 1.5 to 2% of the block or stringer span |
| Automated warehouse, AS/RS | 0.5 in or less |
How deflection is reported
PDS reports the estimated deflection after 30 days of load, because wood keeps deflecting over time (creep). A buyer can add a deflection limit, and PDS then reports the maximum load that stays within it, which can be lower than the strength-based safe working load. In the v5.2 PDS example, a 48x40 racked across its width had a strength rating of 1,630 lb but only 1,006 lb at a 0.75 in deflection limit.
Why deflection matters
Too much sag can let a pallet slip off rack beams, jam conveyors and automated systems, and crush the bottom layer of cartons. Deflection falls with stiffer members: deeper stringers, thicker deckboards, denser species and shorter spans. See pallet deflection and racking pallets.
Questions
- How much pallet deflection is acceptable?
- In racking, about 2% of the span is a common limit, roughly 0.75 in on a 44 in span. Automated systems often need 0.5 in or less.
- Can a pallet pass on strength but fail on deflection?
- Yes. A pallet can be strong enough not to break yet sag too much for racks or conveyors, so ask for both checks.