Deflection
Also called: sag, pallet deflection, bending deflection
Deflection is the amount a pallet bends or sags under load, measured at the point of greatest movement. Racking limits are commonly about 2% of the span, and automated systems often require 0.5 in (13 mm) or less.
In depth: Pallet racking and deflection: rack spans, direction and sag limits
Deflection is a stiffness problem, not a strength problem. A pallet can be strong enough not to break and still sag enough to jam a conveyor, snag a shuttle or let a load slide off a beam.
Typical limits
| Situation | Typical limit |
|---|---|
| Rack, ASTM D1185 test | 1.9% of the distance between supports |
| Rack, ISO 8611 test | 2% of the distance between supports |
| Rack, 44 in (1118 mm) span at 1.9% | About 0.84 in (21 mm) |
| Floor (block or stringer span) | 1.5 to 2% of the span |
| Automated warehouses | 0.5 in (13 mm) or less |
How it is reported
PDS reports "Deflection at Maximum Load" as the estimated deflection after 30 days of creep. If you enter a user deflection limit, PDS also reports the lower "Maximum Load for Deflection Limit". ASTM D1185 measures deflection after a creep period; the Virginia Tech Center for Packaging and Unit Load Design notes that D1185 requires only a two-hour creep test.
Why it matters
Too much deflection causes cases to shift, stretch wrap to tear, and pallets to catch on rack beams or conveyor rollers. For automated storage, deflection usually governs the design.
On a spec sheet or RFQ
State the limit in inches or millimeters, or as a percentage of span, for each support condition, and the load duration (hours, days or weeks).
Common confusions
Deflection in a rack rating is at the rated load, not at failure. Wood deflects less when dry. Plastic deflects more when warm.
Related
- GuidesPallet racking and deflection: rack spans, direction and sag limitsIn a rack a pallet spans between two beams with nothing underneath, so it bends. Racked across the length (stringers span about 40 to 44 in on a 48 in pallet) is usually stiffer than across the width (deckboards span about 36 in). Common deflection limits are about 2% of span, or 0.5 in or less for automated storage.
- GlossaryStiffnessStiffness is a pallet's resistance to bending under load, the inverse of how much it deflects. It depends mostly on the depth of the stringers or deckboards, the material's modulus of elasticity, moisture content and temperature.
- GlossaryCreepCreep is the gradual increase in a pallet's deflection while a load stays on it over time. Wood creeps, and plastic creeps much more, especially when warm, so racked pallets sag more after days or weeks than when first loaded.
- GlossaryRacking loadRacking load is the weight a pallet can safely carry while it spans the gap between rack beams with no support underneath. It is usually the lowest of a pallet's ratings and depends on the span, the direction racked and the number of beams.
- StandardsASTM D1185: test methods for palletsASTM D1185 is the US test method for pallets and related structures (skids, bases, platforms and bins). Static tests estimate stiffness, strength and safe working loads; dynamic tests estimate durability in handling. Retailers such as Home Depot accept an ASTM D1185 test as an alternative to a PDS report.
- StandardsISO 8611: flat pallet test methods, performance and working loadsISO 8611 is the international standard for testing new flat pallets. Part 1 gives the test methods, Part 2 the performance requirements used to set a nominal load, and Part 3 how to determine the maximum working load for a known payload and support condition. Parts 1 and 2 were revised in 2025; Part 3 dates from 2011.
More in Performance and engineering
- GlossaryConcentrated loadA concentrated load is a load that bears on one or a few small areas of the pallet deck instead of spreading over it, such as drums, machinery feet or a coil. It usually gives a much lower safe load than the same weight spread evenly.
- GlossaryDurabilityDurability is a pallet's ability to survive repeated handling, measured as the number of trips or handling cycles before it needs repair or is scrapped. It is driven by fastener quality, lead board width, member thickness and species density.
- GlossaryDynamic loadDynamic load is the weight a pallet can safely carry while it is being moved, supported on forklift tines, a pallet jack or a conveyor. It sits between the static rating and the racking rating.
- GlossaryLoad bridgingLoad bridging is the effect of a stiff unit load spanning across the pallet's weak points, so the packaged product carries part of the load and the pallet deflects and stresses less than it would under a flexible load of the same weight.
- GlossaryLoad capacityLoad capacity is the maximum weight a pallet can safely carry under a stated support condition. It is always quoted per condition: static (on the floor), dynamic (on forks or a pallet jack) and racking (spanning rack beams), and the racking figure is usually the lowest.
- GlossaryPallet tripA pallet trip is one complete cycle of use: the pallet is loaded, moved through the supply chain, unloaded, and made available for its next load. Durability and cost per use are both measured in trips.
Last reviewed 2026-09-24. 269 words.