Box Strength Guide: ECT vs Mullen (Burst) Ratings and Max Weight

Packaging Reference

Box Strength Guide: ECT vs Mullen (Burst) Ratings and Max Weight

Corrugated box strength is measured two ways: Edge Crush Test (ECT), which gauges stacking strength, and the Mullen or burst test, which gauges puncture resistance. This guide lines up the common ratings side by side with general weight guidance so you can pick the right board for the load.

ECT measures resistance to stacking pressure on the edge; the Mullen test measures resistance to a force bursting through the face. They measure different things, so there is no exact conversion.

Single wall: ECT vs Mullen and max weight

Single-wall board covers most everyday parcels. Values below are common industry equivalencies; ECT and burst are not directly convertible, so treat these as general planning guides.

Single-wall corrugated: common ECT ratings, approximate Mullen equivalent, and general max gross weight.
ECT Approx. Mullen (burst) General max weight Common use
23 ECT commonly around 125# burst up to about 20 lb Light retail items, small low-weight parcels
26 ECT commonly around 150# burst up to about 35 lb Light shipping, books, small accessories
29 ECT commonly around 175# burst up to about 50 lb General light shipping, apparel, soft goods
32 ECT commonly around 200# burst up to about 65 lb The everyday standard for most e-commerce parcels
40 ECT commonly around 250# burst up to about 80 lb Denser products, heavier retail cases
44 ECT commonly around 275# burst up to about 95 lb Heavier single items, denser products, sturdier cartons
55 ECT commonly around 350# burst up to about 120 lb Heavy-duty single-wall for dense or industrial goods

Double wall: ECT vs Mullen and max weight

Double-wall board adds a second fluted layer for heavy, dense, or long-transit shipments.

Double-wall corrugated: common ECT ratings, approximate Mullen equivalent, and general max gross weight.
ECT Approx. Mullen (burst) General max weight Common use
48 ECT commonly around 275# burst up to about 100 lb Heavier shipments, moderate industrial parts
51 ECT commonly around 350# burst up to about 120 lb Dense products, machinery parts, bulk cases
61 ECT commonly around 400# burst up to about 140 lb Heavy industrial goods, palletized freight
71 ECT commonly around 500# burst up to about 160 lb Very heavy or high-value dense freight
Why there is no exact conversion: ECT and Mullen measure different failure modes, stacking strength versus bursting strength, so the pairings above are common equivalencies, not fixed conversions. ECT values are typically given as a minimum, and a corrugator may reach the same rating with different board recipes. Max weights are general guidance for a standard-size box in good condition; long journeys, humidity, and poor stacking all reduce real-world capacity.

Which rating for what

Quick picker: matching common loads to a board choice.
Your shipment A common choice
Light apparel, soft goods, small parcels 29 to 32 ECT single wall
Everyday e-commerce, mixed merchandise 32 ECT single wall
Dense or heavier single items 44 ECT single wall
Heavy, fragile, or long-transit goods 48 to 51 ECT double wall
Industrial, palletized, or very heavy freight 61 to 71 ECT double wall

How to use this guide

Start with the gross weight of your packed box, contents plus dunnage, then find the row on the single-wall table that clears it with margin. If the box will be stacked, shipped long distances, or exposed to humidity, step up a rating or move to double wall, because real-world conditions cut into rated capacity. Use the ECT column for stacking-heavy storage and the burst column when puncture and rough handling are the bigger risk. When in doubt between two ratings, the higher one costs little more and protects against the variables you cannot control.

Frequently asked questions

What is the difference between ECT and Mullen?
ECT (Edge Crush Test) measures how much stacking pressure the board edge can take before it crushes, which predicts stacking strength. The Mullen or burst test measures how much force it takes to puncture the board face, which predicts resistance to rough handling. They test different failure modes.
Is 32 ECT the same as 200# burst?
They are commonly treated as equivalent grades, but not as a direct conversion. 32 ECT and 200# Mullen are the usual single-wall standard for everyday parcels, yet each measures a different property, so the pairing is a convention rather than an exact math conversion.
What ECT rating do I need?
For most e-commerce parcels, 32 ECT single wall is the common standard, handling roughly up to 65 lb. Heavier or denser loads step up to 44 ECT single wall or a double-wall board. Match the rating to the packed weight and handling conditions.
When should I choose double wall over single wall?
Choose double wall for heavy contents, fragile goods, long or rough transit, or when boxes will be stacked high in storage. The second fluted layer adds crush and burst resistance beyond what single wall provides.
Does a bigger box need a higher ECT?
Not automatically, capacity is set by the board rating and the contents, not the box size. A large light box can use standard board, while a small dense box may need a higher rating. Size the rating to weight and stacking, not footprint.

Match your box to the load

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Not sure on size yet? Pair this with the box size chart to match dimensions and strength together.

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ECT and Mullen equivalencies and weight ranges are general industry references, not fixed conversions, and are provided for planning purposes. Confirm the rating and capacity of the specific board you order for your shipment and handling conditions.