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Bulk bags come in all shapes and sizes, but even two with very similar designs can have different usable volumes. The chosen attachments and optional extras obviously play a role in this difference, but so too does the type of product being placed in the bags and even the way in which the bags are filled. You need to factor in these unique characteristics in order to get the most out of your bulk bags.

When dealing with bulk quantities of material, even a minuscule difference in estimated volume can have a large impact on the number of bulk bags required. A bulk bag’s volume will determine the shipping and storage decisions that you need to make, so understanding how this capacity can change with certain design elements will enable you to accurately predict the number of bags that you will need.

Custom Bulk Bags is a leading manufacturer and supplier of bulk bags in South Africa. Our products range in dimensions and capacity. We also offer numerous optional extras to suit your unique requirements. All of our bulk bags meet international standards for safety and design, and they all have a minimum 5:1 safety factor as standard.

Everything you need to know about breathable bulk bags

Design affects usable volume

The dimensions of a bulk bag are the major determining factor of volume, naturally. When placing an order with Custom Bulk Bags, you will be able to choose between capacities of half a cubic metre and two cubic metres. This allows you to store between 500kg and two tonnes of material in a single bag.

Once you’ve done the basic mathematics to determine the dimensions of the bulk bags, you will then need to select specific design features and attachments. These can change the basic capacity slightly.

  • Rounding – Our bulk bags are cubic in shape, but when filled, they can experience rounding. This means that the bulk bag will actually store slightly more material than its cubic capacity. Rounding is more pronounced in larger bags with more side area and height. This gives them a slightly cylindrical shape when filled.
  • Inlet type – The type of spout at the top of the bulk bag can also affect usable volume. If you opt for a conical top, for example, it will increase the usable volume over a flat top. Different inlets are usually chosen according to the machinery that you use to fill the bags, but they can change the capacity too.
  • Lifting loops – Yes, even the handles of a bulk bag can affect its capacity. This is due to clearance underneath your filling equipment. The industry norm for loops is about 30cm, but if you require longer loops, then the bags will need to be made slightly shorter to accommodate this additional clearance.

Consult with your bulk bag supplier

Luckily, your bulk bag supplier should be able to guide you along these design choices and calculations. Custom Bulk Bags will consult with customers to ensure that they get the ideal products for their needs. We can help you determine the best attachments and design elements, as well as how these will impact usable volume. For more information about our bulk bags, please contact us today. 


Custom Bulk Bags is a leading South African manufacturer of woven polypropylene bags for various industries, such as mining, chemicals and food. We are able to produce over 3.5-million bulk bags per year, keeping our customers in stock at all times. Our bags adhere to the highest levels of quality as a result of our stringent in-house testing and quality control programmes.

Custom Bulk Bags holds ISO 9001 certification and we currently have a number of UN-certified designs. We are a Level 3 B-BBEE manufacturer and supplier and fall under the ownership structure of Deneb Investments Limited. For more information on our products, contact Follow us on Facebook for our latest news and industry insights.