Edge crush test (ECT)
ECT measures the edgewise compressive strength of a corrugated board, reported in pounds per inch or kN/m. It is the standard predictor of stacking strength and has largely replaced burst strength as the spec for box certification.
The test cuts a small rectangular board sample and compresses it on edge until it crushes. The peak load divided by the sample width is the ECT value. A 44 ECT board has a 44-pound-per-inch edgewise strength.
ECT predicts how a stack of identical boxes will perform under their own weight on a pallet — much more directly than burst strength, which measures rupture resistance under perpendicular pressure. For e-commerce and warehouse stacking applications, ECT is the more useful spec.
The Box Maker's Certificate stamp on the bottom flap of most corrugated boxes shows the ECT value (and sometimes the older burst value as well). Spec sheets and order documents typically reference ECT for box-strength requirements.
Related terms
- Burst strength (Mullen)Burst strength is the pressure required to rupture a paper or board sample, applied through a rubber diaphragm by a Mullen tester. It is reported in psi or kPa and is one of the oldest standardised paper strength tests.
- LinerboardLinerboard is the flat, smooth paper layer bonded to either side of a corrugated medium to form a corrugated board. It provides the strength, printability, and outer surface of a cardboard box.
- Caliper (paper)Caliper is the measure of a paper or board's thickness, typically expressed in thousandths of an inch (points or 'pt') in North America and in micrometres elsewhere. A 12-point board is 0.012 inches thick.
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