Corrugated board grades by ECT
ECT is the load, in pounds per inch of edge, that a strip of board carries standing on edge before it crushes. Because box walls fail the same way, ECT predicts stacking strength, and it is what most US boxes are graded by today.
Grades and estimated strength
| Grade | Wall | Flute pages | Lowest BCT | Highest BCT |
|---|---|---|---|---|
| 23 ECT | single | B, C, E | 253 | 399 |
| 26 ECT | single | B, C, E | 286 | 451 |
| 29 ECT | single | B, C, E | 318 | 504 |
| 32 ECT | single | B, C, E | 351 | 556 |
| 40 ECT | single | B, C, E | 439 | 695 |
| 42 ECT | double | BC, EB | 799 | 979 |
| 44 ECT | single | B, C, E | 483 | 764 |
| 48 ECT | single, double | B, C, E, BC, EB | 527 | 1,118 |
| 51 ECT | double | BC, EB | 970 | 1,188 |
| 55 ECT | single | B, C, E | 604 | 955 |
| 61 ECT | double | BC, EB | 1,160 | 1,421 |
| 71 ECT | double | BC, EB | 1,350 | 1,654 |
| 82 ECT | double | BC, EB | 1,560 | 1,910 |
| 90 ECT | triple | AAC | 2,882 | 2,882 |
| 112 ECT | triple | AAC | 3,586 | 3,586 |
The list is the set of ECT values Packgent computes for, not a statement of what every mill makes. Burst-graded (Mullen) boards and the NMFC Item 222 limits that link the two scales are pending verification.
Sources
- TAPPI T 811: Edgewise compressive strength of corrugated fibreboard (short column test)
- McKee, Gander & Wachuta (1963), Paperboard Packaging 48(8)
Last reviewed . See all sources and how Packgent computes.