Box strength: ECT vs Mullen
ECT (edge crush test) measures how much stacking load a box's board can take; Mullen (burst test) measures how hard you must push to puncture it. The common single-wall grades are roughly equivalent: 32 ECT ≈ 200# Mullen, typically for boxes up to about 40 lb, and 44 ECT ≈ 275# for up to about 65 lb.
Two ways to rate a box
Corrugated boxes in North America carry a box maker's certificate, a round stamp on the bottom flap. It shows either an ECT value (pounds per inch of edge before the board crushes) or a bursting test in pounds per square inch, the Mullen rating, plus the maximum size and gross weight the box is meant for.
Equivalent grades
| ECT | Mullen (burst) | Board | Typical max weight |
|---|---|---|---|
| 29 ECT | 175# | Single wall | about 30 lb |
| 32 ECT | 200# | Single wall | about 40 lb |
| 44 ECT | 275# | Single wall | about 65 lb |
| 48 ECT | 275# double wall | Double wall | about 80 lb |
| 51 ECT | 350# | Double wall | about 95 lb |
| 61 ECT | 500# | Double wall | about 120 lb |
| 71 ECT | 600# / 1100# triple wall | Double or triple | about 140 lb and up |
Equivalents and weights are approximate industry rules of thumb; the box maker's certificate on your carton states its own limits.
Which one do you need?
- Palletised, stacked freight: ECT matters most, because the bottom carton carries everything above it.
- Parcels thrown through sorting hubs: burst strength (Mullen) resists punctures.
- Export by sea: humidity in containers can cut board strength by a third or more; choose a higher grade or double wall.
- Heavy single items: double wall and internal supports.
Stacking strength in practice
A carton's compression strength comes from its corners and walls. Column stacking keeps that load straight; interlocking layers, overhang off the pallet edge and handholes all reduce it. See pallet stacking patterns.
Board outside North America
Elsewhere board is usually specified by flute (B, C, BC double wall) and paper grammage, and tested with BCT (box compression) or ECT methods. Ask the carton supplier for the BCT value of the finished box and compare it with the load from your stack height.
Plan the stack heightLayers per pallet tell you the load on the bottom carton.Tools used in this guide
Related guides
Common questions
What does 32 ECT mean?
The board can withstand 32 pounds per inch of edge before crushing. 32 ECT single wall is the standard shipping box, typically for up to about 40 lb.
Is 32 ECT the same as 200# test?
They are commonly treated as equivalent single-wall grades, but they measure different things: ECT stacking strength, 200# test burst strength.
What is Mullen test?
A bursting test: the pressure in psi needed to rupture the board. A 200# box needs 200 psi to burst.
When should I use double wall boxes?
For heavy goods, export shipments in humid containers, long-term warehouse stacking, or cartons that carry many layers on a pallet.