When choosing a backpack, what should be the first factor to consider? Using capacity as an initial filter to determine whether the backpack size meets your trip and needs is usually the most intuitive first step for most people. However, different brands have varying labeling standards. This may be due to differences in calculation methods, or because some backpacks include stretchable, open-ended pockets that cannot be fully closed, which affects the total capacity measurement. As a result, many people may feel confused about the labeled capacity when selecting a backpack.
This article explains HANCHOR’s measurement methods and standards, helping everyone better understand the origin of these capacity labels and choose the backpack that suits them best.
HANCHOR initially calculates backpack capacity mathematically. For backpacks shaped like cylinders or rectangular prisms, the calculation is straightforward. However, as backpacks become more curved or irregular in shape, it becomes more challenging, and estimates must rely on experience rather than a fixed standard.
To provide a more consistent reference for backpack capacity, HANCHOR follows the measurement method recommended by ASTM (American Society for Testing and Materials, one of the world’s largest standardization organizations). ASTM sets standards for various materials, products, systems, and services, serving as a global benchmark for high-quality design, production, and trade across multiple fields.
The ASTM method for measuring backpack volume, titled “Standard Test Method for Measurement of Backpack Capacity,” includes several key rules:
1. This standard applies to waist packs, soft canvas backpacks, internal- or external-frame backpacks, duffel bags, travel backpacks, and similar types.
2. It provides a unified guideline for manufacturers and consumers to measure backpack volume consistently.
3. Unenclosed spaces on the backpack, such as open mesh pockets or common side water bottle holders, are not included in the volume calculation.
4. This measurement method is not suitable for backpacks with a total volume smaller than 4 liters.
Materials required for measurement:
* 15–20 mm rigid, non-compressible spheres
* A tall, narrow cylindrical container with a base diameter of 14–18 inches
* A disk that fits inside the cylinder to press down the spheres and easily measure their height
* A tape measure
Measurement Method Explanation:
This method essentially uses plastic spheres to simulate items packed inside a backpack. These fixed-size spheres can be easily poured into a cylinder to calculate the space they occupy.
To measure backpack capacity using this method:
Fill all compartments of the backpack—including the main compartment, top pocket, and external pockets—with 15–20 mm diameter plastic spheres.
Ensure all compression straps are fully loosened so the backpack is at its maximum capacity during measurement.
When filling the spheres, pay attention to all corners and fill to the limit that still allows the backpack opening to close.
Prepare a tall, narrow cylindrical container (14–18 inches in diameter), and pour all the spheres from the backpack into it.
Use a disk to compress the spheres evenly, then measure the horizontal height.
Calculate the backpack volume using the cylinder volume formula below:
Volume = height X (diameter 2) X 3.1416 / 4
HANCHOR re-measured the capacity of all its backpack series using international standards and also outlined several measurement guidelines for reference:
* For backpacks between 4L and 10L, measure at least three units of the same model and take the average capacity.
* When measuring roll-top backpacks, the opening should be rolled and closed with three folds to determine the maximum capacity.
* The basic capacity is measured from the bottom of the backpack up to the top edge of the back panel; any space above the back panel is considered the backpack’s extended capacity.
* This method provides the basic capacity up to the back panel while also indicating the maximum extended volume, helping consumers better assess their needs.
* Following ASTM standards, pockets that cannot be fully closed are not included in the capacity measurement.
* Models like MARBLE, CHERT, COBBLE, and ASH can be used as frameless backpacks; therefore, their capacity is measured without adding the back panel or aluminum frame to determine the maximum volume.
After this series of measurements, the volume list of HANCHOR backpacks has been finalized. This information will also be updated in the product specifications to provide the most up-to-date details.
