If you've ever received a shipment where the bottom boxes were crushed by the weight of the boxes above them, you've witnessed an ECT failure. Edge Crush Test is the single most important specification for corrugated box performance, yet many buyers don't know what it means.
What ECT Measures
Edge Crush Test measures the amount of force (in pounds per linear inch) required to crush a sample of corrugated board standing on its edge. It directly predicts a box's ability to resist compression when stacked.
A higher ECT number means a stronger box. Simple.
Common ECT Ratings
| ECT Rating | Equivalent Burst | Max Stacking Weight | Typical Use |
|---|---|---|---|
| 23 ECT | 125# | Up to 20 lbs per box | Lightweight items, retail |
| 26 ECT | 150# | Up to 35 lbs per box | General purpose |
| 29 ECT | 175# | Up to 50 lbs per box | Medium weight items |
| 32 ECT | 200# | Up to 65 lbs per box | Standard shipping |
| 40 ECT | 275# | Up to 80 lbs per box | Heavy items |
| 44 ECT | 350# | Up to 100 lbs per box | Very heavy items |
| 48 ECT | N/A | Up to 120 lbs per box | Industrial/export |
ECT vs. Mullen Burst Test
Historically, corrugated strength was specified using the Mullen Burst Test (expressed as "200# test" or "275# test"). This measures how much pressure the board can withstand before puncturing.
ECT has largely replaced Mullen as the primary specification because compression (stacking) is a more common cause of box failure than puncturing. However, both ratings appear on box certificates.
Conversion: ECT 32 is approximately equivalent to 200# Mullen. This is the most common rating for general shipping boxes.
Why ECT Matters for Used Boxes
When boxes are used multiple times, their ECT rating gradually decreases. The corrugated flutes compress slightly under load, and the fibers lose some elasticity. A box that started at ECT 32 might perform at ECT 26–28 after one or two use cycles.
- Grade A used boxes retain 90%+ of their original ECT performance
- Grade B boxes retain approximately 75–85%
- Grade C boxes may retain only 60–75%
For critical stacking applications, we recommend used Grade A boxes or stepping up one ECT level from what you'd specify for new boxes. For example, if you'd normally use ECT 32 new boxes, consider Grade A used boxes that were originally ECT 40.
How to Check ECT
The ECT rating is printed on the box maker's certificate — the circular stamp typically found on the bottom flap of the box. Look for a number followed by "ECT" (e.g., "32 ECT").
If the stamp has faded or been removed (common with used boxes), you can request ECT testing from the supplier. At EcoBoxes NY, we test random samples from each batch and can provide ECT data on request.
Practical Guidelines
- E-commerce (under 10 lbs): 23 ECT is sufficient
- General shipping (10–30 lbs): 32 ECT is the safe standard
- Heavy items (30–60 lbs): 40 ECT minimum
- Very heavy (60+ lbs): 44+ ECT or double-wall construction
- Stacking 5+ high: Add one ECT level above the minimum
When in doubt, go up one ECT level. The cost difference between ECT ratings is minimal ($0.10–$0.30 per box), but the protection difference is significant.