Safety factor
Also called: factor of safety, design factor
A safety factor is the ratio between the load that causes a pallet to fail and the safe load it is rated for. ISO 8611 divides the ultimate load by 2 and ASTM D1185 by 2.84, before deflection checks; PDS uses reliability-based safety levels instead of a single factor.
In depth: ISO 8611: flat pallet test methods, performance and working loads
A safety factor covers what the rating cannot see: variation in lumber, fastener quality, load placement, impacts and wear. It turns a failure load into a working load.
Values in use
| Method | Safety factor on ultimate load |
|---|---|
| ISO 8611 | 2 |
| ASTM D1185 | 2.84 |
| PDS | Reliability-based; depends on load weight variability |
The ISO and ASTM values are as summarized by the Virginia Tech Center for Packaging and Unit Load Design. In both test methods, the strength-based figure is then checked against a deflection limit, and the lower result becomes the safe load.
How PDS handles it
PDS asks for load weight variability: Low (coefficient of variation 10%), Medium (25%), High (45%) or user-specified. Higher variability means some loads will be much heavier than average, so the calculated safe load drops. There is no single factor to quote.
Why it matters
Two pallets with the same claimed capacity can have very different margins if one was rated with a factor of 2 and the other with 2.84. That is one reason test results from different standards should not be compared directly.
On a spec sheet or RFQ
Ask which method produced the rating. If you have your own requirement (for example a customer's minimum safe working load), state it as a safe load in each support condition, not as a failure load.
Common confusions
A rating is not "safe load × factor = what it can really hold". Wood strength varies, and the factor is not spare capacity to plan into.
Related
- GlossarySafe loadSafe load (safe working load, SWL) is the largest load a pallet should carry in a given support condition, set well below the load that breaks it. Test standards divide the ultimate load by a safety factor, and PDS uses reliability-based safety levels.
- 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.
- 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.
- 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.
- GuidesHow much weight can a pallet hold? Static, dynamic and racking capacityIt depends on how the pallet is supported. A typical 48 × 40 wood pallet safely carries about 1,500 to 2,800 lb (680 to 1,270 kg) in racking or on forks, and several times that on a flat floor. A EUR pallet is rated 1,500 kg. Only the manufacturer's rating for your support condition is authoritative.
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.
- 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.
- GlossaryDeflectionDeflection 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.
- 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.
Last reviewed 2026-09-24. 267 words.