While the weight a box can hold may not be top of mind for anyone making a one-off purchase, the weight and strength of a corrugated box can strongly impact the bottom line. Finding the appropriate weight and strength for a corrugated box can mean lower costs in the supply chain and more profit for a business.

Corrugated boxes are made of three different layers of paper: an inside liner, an outside liner and fluting which runs in between. The flutes between the layers of liners give strength and structure to corrugated boxes and provide an extra layer of protection. This corrugated method, also known as containerboard, ultimately helps provide the strength needed to hold weight and protect the product inside.

The strength of a corrugated box starts with its material. A box’s strength is relative to its density. The more walls a box has, the stronger it will be. The manufacturer’s stamp inside the box usually states single wall, double wall, or triple wall to let you know the strength of the box.

Because all corrugated boxes are not made the same, the outer and inner dimensions may vary, meaning that the weight the box is able to carry can also vary. Calculating the box size also allows businesses to make informed decisions about logistics and supply chain management, but box size will not affect the strength of the box overall.

Even though it may be tempting to simply measure from the outside, box size is always given in terms of inner dimensions. Usually, length is mentioned first, or the longest dimension of the opening, followed by the width and depth.

Ideally, corrugated boxes maintain a proportion of 2:1:2 (L:W:D). However, corrugated boxes of different dimensions are absolutely available for products that do not fit in standard sizes.

For boxes of all sizes, calculating the weight that can be held by the corrugation is done by something called the edge-crush test (ECT). “ECT is a measure of the compressive strength of corrugated board. It is measured by compressing a small segment of board on edge between two rigid plates perpendicular to the direction of the flutes until a peak load is established.”

Compared to previous industry standards, using ECT-rated corrugated boxes results in fewer raw materials, lower energy requirements, and reduced pollution, in all stages of the package’s life cycle.

To calculate the weight that a corrugated box can hold, the ECT rating is essential. On the bottom of nearly every shipping box, there will be a Box Maker’s Certificate. There will be a number corresponding to the “Edge Crush Test”.

 

Below are estimates for the amount of weight a single-wall corrugated box can hold based on the ECT number found on the bottom of the box.

ECT#           Weight able to be held in pounds (lbs)

32                30

40                40

44                50

55                65

 

A double-wall corrugated box can hold the below weight based on the ECT number found on the bottom of the box.

ECT#           Weight able to be held in pounds (lbs)

48                60

51                80

61                100

71                120

82                140

 

Based on these calculations, businesses can make informed financial decisions as to how much product to place in a box or how large of a corrugated box is needed to meet their needs.

We, here at Brown & Pratt, have over 40 years of combined experience to help you determine what style of corrugated box will best suit your packaging needs. There are 30-plus styles of corrugated boxes. From basic Regular Slotted Containers (RSC) to self-erecting boxes to retail floor displays, we have the corrugated box you need. We’ll combine our experience with your box needs and budget to satisfy your corrugated application.