Hi! This is KUMIBOX.

Day to day, we support designers by digging through specifications and standards to find ideal solutions. Today, however, we’re stepping out of our role to talk to you as a colleague from the industry.

Corrugated Board Quality Testing: BCT, ECT, and Why It’s the FOUNDATION of Your Packaging

Corrugated board is a brilliantly simple yet mechanically sophisticated material. But how can we be sure that packaging will survive transport and stacking? That your pallet of goods won’t collapse somewhere in the client’s warehouse?

The answer lies in testing — specifically in two fundamental parameters: BCT and ECT.

1. ECT (Edge Crush Test) — Strength of the Material

ECT measures the compressive strength of corrugated board parallel to the flutes. It’s a destructive test that tells us how strong the raw material is.

Why it matters: The vertical flutes carry the majority of the load. A higher ECT means a stiffer board — and a stronger box structure overall.

2. BCT (Box Compression Test) — Strength of the Finished Box

BCT measures how much compressive load a finished box can withstand before collapsing. If ECT is about the “brick,” BCT is about the entire “house.”

Why it matters: This is the number that determines stacking strength and warehouse safety. It answers the question: how many layers can be safely stacked on a pallet?

3. The McKee Formula — Connecting ECT and BCT

The McKee formula allows us to predict BCT based on measurable board parameters — eliminating the need to test every prototype.

1. ECT (material strength)
2. Board thickness (e.g., 3 mm for B-flute, 4 mm for C-flute)
3. Box perimeter (2L + 2W)

With these inputs, we can calculate expected box compression strength and choose raw materials accordingly — optimizing for both performance and cost.

4. The Catch — Lab BCT ≠ Real-World BCT

A lab test gives ideal numbers — but real-world conditions reduce strength dramatically. Here’s what affects it:

• Humidity: Corrugated absorbs moisture. High humidity can reduce BCT by up to 60% .
• Storage time: Compression strength decreases over time as material “creeps.”
• Palletization pattern: Interlocking stacking reduces strength vs. column stacking.
• Pallet overhang: Even 1 cm overhang drastically lowers load-bearing capacity.

A lab result of 300 kg might translate to only 120 kg after a month in humid warehouse conditions — well below the intended load.

That’s a recipe for failure.

5. Designing for Real Conditions

Designers must include safety factors accounting for humidity, time, stacking pattern, and palletization. Manual calculation is complex — but essential.

Modern palletization software bridges theory and practice — it simulates real-world conditions using actual BCT data . That’s the only way to ensure structural safety and packaging efficiency.

Remember: ECT and BCT are not just numbers. They are the language of packaging performance and safety.

Stay strong!
— The KUMIBOX Team