SC Steve Clery

ECT vs. Mullen (Burst Test)

Two different tests, on two different Box Manufacturer’s Certificates, measuring two different kinds of failure. What each one actually tells you — and why they aren’t directly convertible.

What each test measures

ECT — Edge Crush Test

Measures a board’s resistance to edge-on compression: how much force per lineal inch it can take before it crushes when stood on its edge. This is what predicts stacking strength — how many boxes or pallets can be stacked before the bottom box fails — and is the direct input to compression-prediction formulas like McKee.

Mullen — Burst Test

Measures how much internal pressure a board can withstand before it punctures or bursts, similar to a diaphragm being pushed until it fails. It correlates with rough-handling puncture resistance more than with stacking strength.

Because these two tests measure different failure modes on different geometries, there’s no reliable mathematical conversion between an ECT number and a Mullen number. A board can carry a strong Mullen rating and a comparatively weaker ECT, or the reverse, depending on how it’s constructed.

Which one matters for stacking

Most modern Box Manufacturer’s Certificates show ECT, because ECT correlates with stacking performance — the failure mode that actually matters in a warehouse or on a truck (bottom-box crush). Mullen certification is older and still shows up on some retail and rail-freight requirements, but it doesn’t tell you whether your bottom box will survive a stack.

If you only have a Mullen number and need to know stacking strength, the honest answer is to get an ECT number — from your supplier’s spec or a real compression test — rather than estimating one from Mullen. There isn’t a reliable formula for that conversion, and guessing understates real risk.

The Warehouse Stacking Calculator uses ECT and the McKee formula to check whether a box combination is strong enough for your stack — try it with your own numbers. For how flute type affects the caliper side of that formula, see Flute Types Explained.

ECT vs. Mullen questions

Is ECT the same as Mullen (burst test)?
No — they measure different things. ECT (Edge Crush Test) measures a board's resistance to edge-on compression, which is what predicts stacking strength. Mullen (burst test) measures resistance to puncture/rupture. Most modern Box Manufacturer's Certificates use ECT because it correlates with stacking performance.
Can I convert a Mullen rating to an ECT number?
Not reliably. They measure different failure modes on different test geometries, so there's no accepted formula to convert one to the other. If you need an ECT number for a stacking calculation, get it from the box's actual certificate or a real test — don't back into an estimate from a Mullen rating.
Why did the industry move from Mullen to ECT?
As distribution shifted toward taller stacks, longer storage, and more automated handling, stacking failure (bottom-box crush) became a more common real-world failure mode than puncture — and ECT predicts that failure mode directly, through formulas like McKee, in a way Mullen doesn't. That's why most modern Box Manufacturer's Certificates lead with ECT.
Do ECT and Mullen replace a real compression test?
No — both are certification standards for the board itself, and formulas like McKee use ECT to predict expected box performance from it. Neither substitutes for an actual compression test on your finished box, product, and packing configuration when the application is critical or borderline.