Static compression measures the maximum load a pallet can support when stacked without movement.
Detailed Definition
Static compression describes how a pallet behaves when it carries a load while sitting still on a flat, fully supporting surface, such as the floor or the bottom position in a stack. Standard pallet test methods, including ASTM D1185 and ISO 8611, include compression tests that apply load to the pallet and measure deformation. The results help set the pallet's static, floor-stacked capacity, which is usually the highest of its ratings because the floor supports the whole pallet. Dynamic and racked ratings are normally lower.
Static, dynamic and racked ratings
A pallet usually has three different capacities. The static rating applies when the pallet sits still on a flat floor, often at the bottom of a stack. The dynamic rating applies while the loaded pallet is lifted and moved by forklift or pallet jack. The racked rating applies when it spans rack beams with no support in between. The same pallet can carry very different loads in each case, so a single capacity number without the support condition is incomplete.
What compression does to a pallet
Under static load, the stress concentrates in the stringers or blocks and in the bottom deck boards between them. Over time, wood can creep, so a load that a pallet holds briefly in a test may cause more deflection if left for months. Concentrated loads, such as a machine on feet, stress the pallet very differently from a uniform load of cartons.
Using static ratings correctly
- For stacking, the bottom pallet carries the weight of every load above it.
- Ask whether the rating assumes a uniform or concentrated load.
- Check that the packaging, not just the pallet, can bear the stack.
- Use the Pallet Design System or testing to confirm capacity for your conditions.
Authoritative Sources
- ASTM International (ASTM): the global standards body that publishes ASTM D1185 (Standard Test Methods for Pallets and Related Structures Employed in Materials Handling and Shipping).
- National Wooden Pallet & Container Association (NWPCA): the US trade association representing wood pallet manufacturers, recyclers, and component producers, founded in 1947.
Related Glossary Terms
Frequently Asked Questions
Can I use a pallet's static rating for rack storage?
No. The static rating assumes the pallet is fully supported on a flat surface. In rack, the pallet spans between beams with nothing underneath, so its deck boards or stringers carry the load in bending. That racked capacity is usually much lower than the static rating. Ask the supplier for a racked capacity that matches your rack orientation and load type, and use that number for rack storage.
How many loaded pallets can I stack on top of each other?
It depends on the static capacity of the bottom pallet, the compression strength of the packaging in each load, how evenly the upper pallets bear on the loads below, the floor, and how long the stack will stand. Humidity weakens corrugated boxes over time. Work out the total weight on the bottom pallet and its load, compare it with the pallet rating and the packaging's stacking strength, and leave a margin.