Weight Capacity of Plywood Boxes

September 6, 2024

Plywood is one result of humanity’s never-ending endeavour to make lighter but stronger materials. It is to wood just as titanium is to metals and spider silk is to biological matter (though the last one is experimental). You can see this engineered wood everywhere, from construction and renovation to timber packaging solutions.

But just how strong is plywood exactly? In this case, how much weight can plywood boxes in Melbourne can handle? Wood isn’t as resilient as steel – that’s a no-brainer, but this is about getting the strongest possible packaging product for the least weight. You’d want a solution that lets you move your goods quickly and safely.

That’s what we’re here to find out today. But first, it pays to know how plywood is made.

From Planks to Plywood

The working concept behind plywood can’t get any simpler: it’s impossible to break a stick in a bundle. In ancient times, people created plywood to cut construction costs (especially when wood was in short supply) while adding aesthetics but later found that it significantly lowered flexing and made it more rigid.

The principles behind creating the material have more or less remained the same over the centuries. Here’s a simplified rundown of the steps.

• Cutting the debarked log into veneer blocks
• Softening the blocks with heat and cutting them
• Applying the glue to each of the cut veneers
• Piling up the veneers in alternating grain directions (cross-graining)
• Subjecting the plywood to a hot press
• Trimming and belt-sanding the excess material

Cross-graining enables the plywood to maintain its strength in every part of the material and reduces the likelihood of splitting when being nailed or screwed. For better balance and reduced risk of warping, plywood almost always consists of an odd number of plies. Three and five-ply plywood (2-4 mm thickness) are the most common.

Plywood can be made out of any type of softwood or hardwood. As we discussed in our blog post about the best wood for creating wooden crates, some common woods used include pine, oak, cedar, and birch.

Beyond Thickness

Thickness or the number of plies is a major consideration when determining a plywood’s weight capacity and, by extension, that of a plywood case or crate. More plies translate to more load-bearing support, but that isn’t the only consideration.

The plywood’s span rating can change how much weight plywood can hold. This refers to the maximum recommended centre-on-centre spacing between two pieces of plywood (in inches) serving as support. A thin plywood with considerable space between the plywood pieces’ centre can support more load than a thick one with only half as much spacing.

Below is a sample calculation to give you a clear idea.

Source: Home Efficiency Guide

It may seem counterintuitive, but a plywood case or crate transfers its content’s load to the ground similar to, well, a building. Aside from having enough thickness, the wooden box must also provide enough room to handle the weight.

The type of wood used is another factor, but there are exceptions. For instance, although hardwood is stronger and can handle bigger loads than softwood, some hardwood species can actually be softer than some softwood ones. The Janka Hardness Value (JHV), which is measured in pounds-force, gauges a specific wood’s resistance to denting.

Here are the JHVs of some of the most common types of wood used in making plywood.

Source: Family Handyman

Essentially, the values indicate how much weight it takes to embed a steel ball 11.28 mm in diameter halfway into the wood. Given that a plywood case deals with the weight of its contents pressing down, the timber’s hardness equally matters.

The glue used to paste the wood veneers together also plays a crucial role. With the right adhesive, even softwood plywood can be as strong as their hardwood counterparts, if not more. Given how plywood crates are used, most manufacturers use Type-A glue, which is the strongest grade of glue in use today.

Conclusion

These factors are by no means the only considerations, but they show how versatile this material can be. With the right design and materials, plywood boxes are capable of holding items several times their weight. It won’t be surprising if such a wooden box can store and transport machine components weighing several hundred kilograms.