What Is ECT?
ECT stands for Edge Crush Test — a standardized measurement of how much top-to-bottom compressive force a corrugated board can withstand before failing. It is measured in pounds per linear inch of board edge.
The ECT rating directly translates to stacking strength: how much weight can be placed on top of a box before it buckles. This is the most important specification when boxes will be palletized and stacked in a warehouse or truck.
The Common Ratings
32 ECT is the standard for single-wall boxes handling up to 40 lbs. It is the default for e-commerce, retail shipping, and general light-duty use. If you are shipping clothing, books, or non-fragile consumer goods, 32 ECT is usually sufficient.
44 ECT is heavy-duty single wall for items in the 40-65 lb range. It provides significantly better stacking strength and is preferred for warehouse storage where boxes sit on shelves or pallets for extended periods.
48 ECT is standard double wall. The jump from 44 to 48 is bigger than the numbers suggest because you are adding an entire layer of fluting. This is for 60-80 lb items and serious stacking requirements.
51 ECT is heavy double wall for loads up to 100 lbs. Used in industrial shipping, export packaging, and heavy equipment.
71 ECT is the maximum commonly available — triple wall construction for loads exceeding 100 lbs. Think automotive parts, industrial machinery, and extremely heavy products.
ECT vs. Burst Strength
Older specifications used "burst strength" measured in pounds per square inch (the # rating, like 200# or 275#). Burst strength measures puncture resistance — how hard you can push a point into the side before it breaks through.
ECT has largely replaced burst strength as the primary specification because stacking performance matters more than puncture resistance in modern supply chains. However, burst strength is still relevant for shipments facing rough handling or point impacts.
How to Choose
The formula is simpler than most people think:
- Under 20 lbs: 32 ECT single wall
- 20-40 lbs: 32 ECT single wall (C-flute preferred)
- 40-65 lbs: 44 ECT single wall or 48 ECT double wall
- 65-100 lbs: 48-51 ECT double wall
- Over 100 lbs: 71 ECT triple wall or gaylord box
When in doubt, go one step up. The cost difference between a 32 ECT and 44 ECT box is typically $0.15-0.30 — far less than a damage claim.