Box Strength Guide: ECT vs Mullen (Burst) Ratings and Max Weight
ECT rates a box for stacking strength, and Mullen, also called the burst test, rates it for puncture resistance. Most ecommerce shipments belong on an ECT rated box, with 32 ECT covering the typical parcel up to about 65 lb. This guide explains when each rating matters and which strength to choose.
What the two ratings measure
ECT, edge crush test
A section of corrugated board is compressed on its edge until it crushes, and the rating is the load it survived in pounds per inch of width. A 32 ECT board withstands 32 lb per inch. Boxes carry stacked weight through their vertical edges, so ECT predicts how a box behaves under other boxes, on a pallet, or on a warehouse shelf.
Mullen, burst test
Hydraulic pressure is applied to the face of the board until it ruptures, and the rating is that pressure in pounds per square inch. A 200# board resists 200 lb per square inch. Burst strength predicts how a box handles point impacts, punctures, and rough sorting, the forces that hit a single box from outside.
When ECT is the right lens
- Parcels moving through modern carrier networks, where boxes ride stacked in containers and on conveyors.
- Anything palletized. The bottom layer carries every layer above it through its edges.
- Warehouse storage, where cartons sit stacked for weeks and slowly settle under load.
- Weight sensitive shipping. ECT grades reach their stacking strength with lighter board, which keeps package weight down.
When Mullen is the right lens
- Loose single boxes in rough parcel or LTL handling, where corners, forks, and neighboring freight strike the box faces.
- Dense contents that push outward against the panels, such as loose hardware or parts that shift in transit.
- Legacy specifications. Older purchasing documents and some freight tariffs are still written around burst values.
Rule of thumb: stacked or palletized, buy on ECT. A single heavy box shipped loose through rough handling, buy on Mullen or step up the wall construction. Not sure, 32 ECT single wall is the grade the standard ecommerce box is built on.
ECT vs Mullen at a glance
| Dimension | ECT (edge crush test) | Mullen (burst test) |
|---|---|---|
| What it measures | Edge compression until the board crushes | Pressure through the face until the board ruptures |
| Units | Pounds per inch of width | Pounds per square inch |
| Predicts | Stacking and compression performance | Puncture and rough handling resistance |
| Best for | Ecommerce parcels, palletized freight, stored inventory | Loose heavy boxes, abusive transit, legacy specs |
| Common grades | 32, 44, 48, 51 ECT | 200#, 275#, 350# |
| Test standard | TAPPI T 811 | TAPPI T 810 |
The two scales do not convert with a formula, but the industry pairs them into duty classes, 32 ECT with 200#, 44 ECT with 275#, and so on through the double wall grades. The full table, including weight guidance for every grade, lives on the ECT to Mullen conversion chart.
Four common scenarios
DTC parcels under 65 lb
Apparel, home goods, and general ecommerce orders travel fine in 32 ECT single wall, the standard parcel grade. Browse 32 ECT box sizes to match dimensions to your product.
Dense or heavy single items
Once box plus contents pushes toward the 95 lb class, think canned goods, hardware, books packed in bulk, step up to 44 ECT boxes so the walls keep their margin.
Palletized or stacked freight
Bottom cartons carry the whole stack for the whole trip. Double wall grades such as 48 ECT boxes hold their rating under sustained load and longer storage.
Rough handling, one box at a time
A single box over 50 lb shipped loose takes face impacts that stacking ratings do not describe. Work through the over 50 lb box strength guide and favor burst rated or double wall board.
Choosing a strength in four steps
- Weigh the packed box, contents plus void fill, not the product alone.
- Name the dominant risk: stacked compression, or abuse of a single box.
- Pick the grade whose weight guidance clears your packed weight with room to spare, and step up for long transit, humidity, or tall stacks.
- Check the certificate stamp on the bottom flap of the box you buy, so the test and rating match what you specified.
Stuck between the two everyday grades, the 32 ECT vs 44 ECT comparison settles that call directly.
FAQ
What does 32 ECT mean?
The board survived an edge crush test load of 32 lb per inch of width. It is the standard single wall grade for ecommerce parcels, with weight guidance of about 65 lb for box plus contents.
Is 32 ECT the same as a 200 lb box?
They are the same duty class, not the same measurement. 200# describes burst pressure per square inch, 32 ECT describes edge load per inch, and carrier rules treat the two grades as equivalent minimums for single wall boxes.
What is a Mullen rated box?
A box certified under the Mullen burst test, with a stamp listing bursting strength in pounds per square inch, such as 200# or 275#. Mullen rated board resists punctures and point impacts, which suits rough single box shipping.
When do I need 44 ECT instead of 32 ECT?
Move up when packed weight approaches the top of the 32 ECT range at about 65 lb, when contents are dense enough to stress the walls, or when boxes will sit stacked in storage. 44 ECT carries guidance of about 95 lb.
Get the boxes
Packrift stocks corrugated boxes across every grade above and ships from five US warehouses.
Ratings, pairings, and weight figures here are industry reference values for planning, not a warranty for a specific shipment. Real capacity drops with humidity, transit time, and stacking, so confirm the certificate on the boxes you order.