Understanding Box Strength: BCT, ECT & What They Mean for Your Product

Corrugated box strength is not a single number — it is a combination of several measurable properties, each relevant to different aspects of product protection. Two tests dominate specification sheets:

Edge Crush Test (ECT) ECT measures the edgewise compression strength of corrugated board — essentially how much load a column of board can bear before buckling. It is expressed in kN/m. A higher ECT value means the board can support more stacking weight before the flutes collapse.

ECT is the most direct predictor of box stacking strength and is the primary specification for boxes that will be palletised and warehoused.

Box Compression Test (BCT) BCT measures the compression strength of a finished box — the actual load the assembled box can bear. BCT is influenced by ECT but also by moisture content, board caliper, box dimensions, and print coverage (inks reduce compression strength).

As a rule of thumb: BCT ≈ 5.87 × ECT × √(Caliper × Perimeter). Understanding this relationship allows our team to engineer the right combination of flute profile, board grade, and box geometry for your specific stacking requirement.

Bursting Strength (BS) A legacy test that measures puncture resistance of the board face. Less predictive of real-world performance than ECT but still specified by many buyers as a pass/fail threshold.

What should you specify? The answer depends on your use case. For heavy products on pallets, specify ECT and required BCT. For products prone to puncture damage, specify BS. For e-commerce applications with minimal stacking, a lighter board with adequate ECT is often sufficient — and more cost-effective.

We work with clients to specify the minimum board grade that safely meets their protection requirements, avoiding over-engineering that adds unnecessary cost and material weight.