Box Strength Guidelines

Box strength is actually a surprisingly complicated and nuanced characteristic! Here, we provide high level guidance for anyone trying to decide if they should use 23ECTB, 32ECTC, 32ECTE or 44ECTC sheets for their  custom corrugated shipping box. If you want to better understand the different factors that impact box strength, check out our detailed Guide to Shipping Boxes

ECT strength (versus an older approach called the "Mullen Test") is a suitable strength rating system for the vast majority of shipping boxes and is the only one that works with boxes that are made with recycled content. EcoEnclose box strengths are all measured in ECT, and most companies who sell shipping boxes are in the same boat.

As you’re trying to determine the best type of corrugated to use for your boxes, start by using this reference from the team of folks that have delivered millions…and millions and millions of packages just like yours – UPS. Even more important than their vast experience is that they are often the folks who will determine whether or not to honor claims on damaged packages! They provide the following recommendations on their website. Check out the following tool to get specific guidance for your package: https://www.ups.com/packaging/?loc=en_US

Note that UPS does not address the 23B material, but based on our own experience, we have added our guidelines to the chart below.

Maximum Weight of Box and Contents (lbs/kg) Recommended Size Limit of Box Length, Width, and Depth Added (inches/cm)* Minimum Bursting Test (lbs per sq. inch/kg per sq. cm) Minimum Edge Crush Test (ECT) (lbs per inch/kg per cm width)
10-20* 30* 125* 23*
30 75 200 32
40 75 200 40
50 85 250 44
65 95 275 55
80 105 350 N/A

*EcoEnclose recommendations; not provided by UPS.

As described above, ECT (or Mullen Test) is just one factor driving the strength of a box itself. 

The box style is also important. Regular Slotted Container (RSC) styles are inherently stronger; while Tab Locking styles are typically not as strong. Also, the bigger the box, the lower its strength. That is to say, a box that is 5x5x5 made with 23ECTB will resist crushing more effectively than the same style box that is 10x10x10 made with the same sheet (23ECTB).

Finally, note that the strength of a sheet and corresponding box is measured by the number (23, 32, 44, etc). The letter (B, C, E, etc) describes the "flutes" of the sheet, and provides information as to thickness of the corrugated. A 32ECT E and 32ECT C box (of the same size and style) will have the same strength. However, the E flute will be much thinner and sleeker. 

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