Packaging ECT To Mullen Conversion
A 32 ECT box is the working equivalent of a 200# Mullen box, 44 ECT pairs with 275#, and 55 ECT pairs with 350# in single wall. The chart below maps every common rating in both directions, with weight guidance and typical uses for each grade.
ECT to Mullen conversion chart
ECT (edge crush test) and Mullen (burst test) measure different failure modes, so there is no formula that turns one number into the other. What the industry uses instead is a set of equivalence classes: board grades that carrier classification rules treat as the same minimum duty. Those pairings are what this chart shows.
| Board | ECT rating | Mullen (burst) equivalent | Weight guidance, box plus contents | Typical use |
|---|---|---|---|---|
| Single wall | 23 ECT | 125# | Up to about 20 lb | Very light retail goods and inserts |
| Single wall | 26 ECT | 150# | Up to about 35 lb | Light parcels, books, accessories |
| Single wall | 29 ECT | 175# | Up to about 50 lb | Apparel and soft goods |
| Single wall | 32 ECT | 200# | Up to about 65 lb | The standard ecommerce shipping box |
| Single wall | 40 ECT | 250# | Up to about 80 lb | Denser products, heavier retail cases |
| Single wall | 44 ECT | 275# | Up to about 95 lb | Heavy or dense single items |
| Single wall | 55 ECT | 350# | Up to about 120 lb | Heavy duty single wall for dense goods |
| Double wall | 48 ECT | 275# | Up to about 100 lb | Heavier shipments, moderate industrial parts |
| Double wall | 51 ECT | 350# | Up to about 120 lb | Dense products, machinery parts, bulk cases |
| Double wall | 61 ECT | 400# | Up to about 140 lb | Heavy industrial and palletized freight |
| Double wall | 71 ECT | 500# | Up to about 160 lb | Very heavy or high value dense freight |
Read the rows as duty classes, not lab conversions. A mill can reach 32 ECT with more than one board recipe, so two 32 ECT boards can burst at different pressures. Weight figures are planning guidance for a box in good condition, not a warranty. Long transit, humidity, and tall stacking all cut into real capacity.
Reading the chart in both directions
- You have a Mullen spec and need a modern box. Find the burst value, match the board type, and buy the ECT grade on that row. A legacy 200# single wall spec maps to 32 ECT.
- You have an ECT box and an old spec sheet asks for burst. Work the same row in reverse, and confirm the board type first, since 275# appears in both the single wall and double wall classes.
- Your packed weight sits near the top of a row. Step up a grade. The guidance figures assume a box in good condition, and real shipments rarely travel in ideal conditions.
How to read your box maker's certificate
Every certified corrugated box carries a box maker's certificate, the round stamp printed on a bottom flap. It tells you which test the box was certified under and what the board is rated to carry, which makes it the fastest way to place any box on the chart above.
- Test line. An ECT certified box lists Edge Crush Test with a value in pounds per inch of width. A Mullen certified box lists Bursting Test with a value in pounds per square inch.
- Board construction. The stamp states single wall, double wall, or triple wall. Match this before comparing strength numbers across specs.
- Size limit. The maximum combined length, width, and depth, in inches, for the certified rating.
- Gross weight limit. The maximum weight of the box and its contents for the certified rating.
Quick check: if the stamp reads Edge Crush Test, use the ECT column of the chart. If it reads Bursting Test, use the Mullen column. A box is certified under one test, not both.
Which rating should you buy on
ECT is the default for modern ecommerce and palletized shipping because stacking strength is what those shipments stress. Mullen still earns its place when a single box takes repeated point impacts, such as rough handling of loose heavy cartons. The ECT vs Mullen box strength guide walks through the full decision with scenarios.
If the choice has already narrowed to the two most common grades, the 32 ECT vs 44 ECT comparison covers that call, and shipments over 50 lb have their own box strength walkthrough.
Find boxes by rating
Packrift stocks corrugated boxes across these grades and ships from five US warehouses. Browse the full corrugated range or jump straight to a rating.
FAQ
Is there an exact formula to convert ECT to Mullen?
No. ECT measures edge compression and Mullen measures burst pressure, two different failure modes. The pairings in the chart are equivalence classes used by carrier rules, not mathematical conversions.
What is the Mullen equivalent of a 32 ECT box?
200# burst is the accepted single wall equivalent. Both grades are treated as the standard parcel class, with weight guidance of about 65 lb for box plus contents.
Is a 275# box the same as 44 ECT?
In single wall, yes, they sit in the same duty class with guidance of about 95 lb. In double wall, 275# corresponds to 48 ECT instead, so match the board construction before swapping specs.
Can I substitute an ECT rated box for a Mullen spec?
Usually. Carrier classification rules accept boxes certified under either test at the matching minimum. If a customer contract or freight tariff names one test specifically, buy a box certified under that test.
ECT and Mullen pairings and weight figures on this page are industry reference values for planning. They describe minimum board grades in good condition, not a guarantee for a specific shipment. Confirm the certificate printed on the boxes you order.