Packaging resource
ECT ratings explained
ECT (Edge Crush Test) is the industry-standard way to measure how much compressive force a corrugated box can handle before it fails. Understanding ECT ratings helps you specify boxes that are strong enough for your product without overpaying for unnecessary board weight.
What the ECT number means
An ECT rating tells you how many pounds of force per linear inch the corrugated board can withstand before the edge collapses. A 32 ECT box, for example, can resist 32 pounds of pressure per inch of edge when force is applied perpendicular to the flute direction.
In practical terms, ECT predicts how well a box will perform when stacked on a pallet, loaded in a truck, or stored in a warehouse. Higher ECT means stronger stacking performance. Most standard corrugated shipping boxes in the U.S. are 32 ECT.
ECT replaced the older Mullen burst test as the primary strength metric for corrugated packaging in the 1990s. Burst strength measures puncture resistance, while ECT measures compression — which is more relevant to how boxes actually fail during shipping and warehousing.
ECT vs. Mullen burst test
ECT (Edge Crush Test)
Measures compression resistance. Indicates how much weight a box can support when stacked. The standard for most corrugated boxes today.
Mullen (Burst Test)
Measures resistance to puncture. Indicates how much force the box wall can withstand from a sharp or pointed impact. Still used for some applications, especially produce and rough-handling environments.
Which one matters more?
For most shipping applications, ECT is the more useful metric because box failure is usually caused by compression (stacking), not puncture. Ask your supplier which test they certify to.
Common ECT ratings and what they handle
The max weight column is a rough guideline — actual performance depends on box dimensions, product distribution, stacking height, humidity, and storage duration. Always discuss specific requirements with your supplier.
23 ECT
Lightweight consumer goods, apparel, books, small e-commerce orders.
29 ECT
Mid-weight consumer products, food items, boxed kits, retail goods.
32 ECT
The most common rating. General shipping, e-commerce, grocery, light industrial.
44 ECT
Heavier products, stacked cases, palletized loads, wholesale distribution.
48 ECT
Heavy consumer goods, appliances, automotive parts, multi-item master cases.
51 ECT
Industrial parts, heavy equipment components, export shipments.
61 ECT
Heavy industrial, machinery parts, produce in bulk, high-stack warehouse pallets.
71 ECT
Wood crate replacement, military-spec packaging, heavy equipment, export containers.
How to choose the right ECT rating
The right ECT rating depends on three main factors: the weight of the product, how many boxes will be stacked on a pallet, and how long the boxes will be stored before use. Boxes that sit in humid warehouses for weeks lose compressive strength over time, so you may need a higher ECT than the product weight alone would suggest.
As a starting point, 32 ECT handles the majority of standard e-commerce and retail shipping. Step up to 44 ECT for heavier products or higher stacking loads. Move to double-wall (48+ ECT) when products exceed 80 pounds or when boxes will be palletized multiple layers high.
- Under 20 lbs, single carton shipments → 23 ECT is often sufficient
- 20–40 lbs, moderate stacking → 29 or 32 ECT
- 40–65 lbs, palletized → 32 or 44 ECT
- 65–100 lbs, heavy stacking or export → 48 ECT double wall
- Over 100 lbs or industrial use → 51+ ECT double wall or triple wall
Over-specifying costs money
It is tempting to default to a higher ECT for safety margin. But heavier board means higher material cost, higher shipping weight, and more waste. If your product is 15 lbs and shipping individually, a 44 ECT box is unnecessary — and more expensive per unit. Let the product weight, stacking plan, and supply chain conditions drive the decision, not guesswork.
What reduces box strength in the real world
ECT is tested under controlled lab conditions. In actual shipping and warehousing, several factors reduce compressive strength from the rated value.
Humidity and moisture
Corrugated board absorbs moisture from the environment. A box stored in a humid warehouse for 30 days can lose 30–50% of its rated compressive strength. Climate-controlled storage or wax-treated board can mitigate this.
Pallet overhang
Boxes that hang over the edge of a pallet lose the support of the pallet surface. Even a 1-inch overhang can reduce effective stacking strength by 15–20%.
Misaligned stacking
Boxes stacked corner-to-corner (column stacked) are strongest. Cross-stacking or offset patterns reduce compressive performance because the load is not aligned with the vertical flutes.
Printing and die-cutting
Large print areas and die-cut openings weaken the box wall. If your box has a large window or perforated panel, the effective ECT in that area is lower than the board rating.
Get the right spec
Talk to suppliers about box strength
Browse the supplier directory to find manufacturers and distributors who can help you spec the right ECT rating for your product, stacking requirements, and shipping conditions.