Did you know that corrugated cardboard is identified by a test which gives the strength and optimal use? Knowing the strength of the corrugated board will tell you how much weight it can support. The board test or Edge Crush Test (ECT) is identified by a 2-digit number which measures the corrugated boards resistance to compression. This information can be found on the class stamp. The class stamp is normally printed on the bottom of a box. See examples of class stamps below: 
These class stamps explain that the strength of the cardboard is 29 lbs per square inch. This means that up to 29 lbs can be applied to a one square inch surface of corrugated board vertically (parallel to the flute), before it starts to collapse. To find out which ECT you need for your box, you can refer to the table below: 
Souce: Fiber Box Handbox.
When in doubt, it is recommended to choose the higher ECT since the strength of the corrugate varies depending on certain factors (how old the board is, the air’s humidity level, the environment in which your box is stored, etc). In addition, your box will have to support the weight of multiple boxes if they are stacked on top of each other. This means that if you stack your boxes 3 high, the bottom box will be supporting the weigh of the two boxes stacked on top, plus their content.
Can’t find a class stamp on your box? This is possible since manufacturers are not required to print the information on the box. Without the information, it might be hard to guess the cardboard strength just by looking at it. Our CorrDesign Team is here to help, contact us! You already know which type of corrugated you need for your box? Buy it now in our online store!