Packaging Reference Library · Materials & Ratings
ECT vs Mullen Burst: Corrugated Box Strength
What the Edge Crush Test and the Mullen burst test each measure, how they appear on the Box Maker's Certificate, and why the two ratings are paired but not interchangeable.
Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.
What it is
Corrugated board is sold by one of two strength ratings. Edge Crush Test (ECT), measured per TAPPI T 811, is the force a short edge-loaded strip of board can carry before crushing, in pounds per inch of edge. It correlates with stacking (compression) strength. Mullen burst, measured per TAPPI T 810, is the pressure needed to rupture the board face, expressed in pounds per square inch (shown as "200#"). It correlates with resistance to rough handling and puncture and depends heavily on liner weight. Carrier classification rules (NMFC Item 222 for motor carriers, UFC Rule 41 for rail) historically allowed boxes to be certified under either method, which is why both appear in the market.
How to identify
- The Box Maker's Certificate (BMC) printed on a bottom flap names the test (Edge Crush Test or Bursting Test), the rating, the size limit and the gross weight limit, plus the box maker and location.
- ECT-certified board is often lighter for the same stacking strength because it can use high-performance or recycled liners.
Commonly paired single-wall grades
| Mullen burst | ECT commonly offered as the alternative | Max gross weight on certificate (lb) |
|---|---|---|
| 125# | 23 ECT | 20 |
| 150# | 26 ECT | 35 |
| 175# | 29 ECT | 50 |
| 200# | 32 ECT | 65 |
| 275# | 44 ECT | 95 |
| 350# | 55 ECT | 120 |
The pairs reflect how the carrier rules grouped the two methods for certification. They are not conversion factors: a 32 ECT box and a 200# box can perform very differently in stacking or in handling.
Key points
- Choose ECT when boxes are palletized and stacked in warehouses (compression is the main risk). Choose burst when boxes travel individually through parcel or LTL networks with heavy handling, or contain dense items that push on the walls.
- Box compression (ASTM D642) depends on ECT, caliper and box perimeter, and drops sharply with humidity and time under load. Design stacks with a safety factor.
- Carrier packaging rules are revised from time to time; confirm the current NMFC/UFC requirements and the carrier's own tariff before relying on a certificate.
- Specify the test method on the purchase spec. "200# or equivalent" invites substitution.
Common mistakes
- Treating 32 ECT as identical to 200# test.
- Ignoring humidity when sizing a box for long-term warehouse stacking.
- Overloading beyond the gross weight on the certificate.
Governing standards: TAPPI T 811; TAPPI T 810; ASTM D642; NMFC Item 222; UFC Rule 41.
Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.