Also known as: ECT, Edgewise Compression Test
The edge crush test (ECT) measures the force a corrugated board edge withstands before crushing, expressed in kN/m or lb/in. Because it tests vertical compression, ECT is the best predictor of how a box performs when stacked in a warehouse or shipping container.
A short section of board is stood on edge and compressed vertically until it buckles. The peak force is the ECT value. It directly reflects how the flutes behave as load-bearing columns.
This makes ECT the relevant figure for stacking. Box compression strength — how much weight a carton supports before collapsing — correlates strongly with ECT, board thickness and box perimeter.
Real-world derating matters. Stacking strength falls substantially with time under load and with humidity: cartons stored for weeks, or in a humid Gujarat monsoon warehouse or a sea container, can lose a large share of their initial compression strength. Designs should carry a safety factor rather than assume the lab figure.
Where boxes are palletised and stacked several high, or shipped in containers, ECT should be part of the specification alongside bursting strength.
Edge Crush Test at a glance
| Unit | kN/m (metric) or lb/in (imperial) |
|---|---|
| Test method | Board sample compressed on edge (TAPPI T811 / ISO 3037) |
| Predicts | Stacking and box compression strength |
| Degraded by | High humidity, long storage under load, poor box fit |
| Design practice | Apply a safety factor over the lab value |
Common questions
Is there an ECT formula or an edge crush test chart I can use?
ECT is measured on a board sample, not calculated from paper alone, but a working ECT formula adds the ring crush values of the two liners to the fluting value multiplied by its take-up factor. The edge crush test chart buyers use most is typical values by construction, and the box compression that follows from a given ECT comes from the McKee formula in the calculator.
Why do my boxes collapse in the warehouse despite good bursting strength?
Because bursting strength measures puncture resistance, not vertical load. Stacking behaviour is governed by ECT, and it degrades with humidity and time under load. If boxes are stacked, specify ECT and design with a safety margin.
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