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  • Writer's pictureBenson Li

How to Measure Backpack Volume: Your Ultimate Guide

Updated: Aug 2, 2023

Have you ever wondered how the volume of a backpack could be ascertained? Whether you're an outdoor enthusiast, a student, or a traveler, knowing the correct way to measure the volume of a backpack is important when choosing the right one for your needs.

It is important for outdoor enthusiasts to understand how backpack volume is measured.

Why bother measuring the backpack volume yourself when the information is already provided by the manufacturer?

You should be aware that different manufacturers use different methods to calculate the volume of their bags. This lack of standardization means that the published data by the manufacturers may not be accurate or directly comparable.

In order to make fair and accurate comparisons during your purchase, having the ability to calculate or verify the volume yourself is extremely useful. This way, you can ensure consistency and make the best choices based on your own measurements.

In this comprehensive guide, we will explain different methods of measuring backpack volume. From the easiest method that you can arrange at home, to a more accurate test used by companies in their manufacturing process, we've got you covered!

3 different methods to measure a backpack:

1) The Easiest Way—Based on Length (L) X Width (W) X Height (H) = Volume formula. All you need is a tape measure or a ruler.

2) The Improved Formula—We offer a NEW option that can provide reasonable volume data without any special setup.

3) The Most Accurate Way—The standard test method commonly used by backpack brands and manufacturers.

Method 1: The Easiest Way

This traditional method is based on the Length (L) X Width (W) X Height (H) = Volume formula. It only requires a tape measure or ruler.

Simply measure the Length, Width and Height of the backpack.

It requires a tape measure or ruler to measure the volume of a backpack.

(Alternatively, you can gather the required measurements from the official websites of the backpack manufacturers.)

Then, use the following formula to determine its volume: Length (L) X Width (W) X Height (H) = Volume

To make it easier for you, I have created the following backpack volume calculator. Just plug in the measurements (L, W & H), and choose between the units (cm or inch), the calculator will then automatically calculate the backpacks volume in cubic centimeters (cm3), cubic inches (in3) or liters (L). I hope it's useful. Let me know if you have any problems with it (

This traditional method of measuring backpack volume is straightforward, but it is not the most accurate method because this Length (L) X Width (W) X Height (H) = Volume formula is for measuring the volume of a box-shaped object, while most backpacks have irregular shapes.

The traditional method of Calculating Volume of a Bag is not so accurate because most backpacks are not in box-shape.

Additionally, the size of the backpack does not necessarily reflect its storage volume. For example, a large backpack may have limited usable storage space due to heavy padding or other design features (e.g. frame). Therefore, when determining the volume of a backpack, it's essential to consider its actual storage volume/capacity rather than its external dimensions.

Despite this, the data from this method can still be meaningful as a reference when comparing volumes of different backpacks before making a purchase decision. It's important to keep in mind that the actual storage volume/capacity is typically 20%-40% less than the result calculated by this method.


Method 2: The Improved Formula

The drawback of using the Length (L) X Width (W) X Height (H) = Volume formula is its inaccuracy. This formula assumes that the backpack has a box-like shape, which may not be the case for most backpacks. As a result, the calculated volume tends to be larger than the actual storage volume/capacity.

To address this issue, we propose using another formula that better approximates the shape of a backpack, specifically, the formula for an elliptic cylinder. Since many backpacks (especially hiking backpack) have a cylindrical appearance, this formula should provide a much closer estimation of the actual volume.

The formula for elliptic cylinder is a better way to Calculate Volume of a Backpack because it matches the shape better.

Formula for the volume of an elliptic cylinder:

V = π abh

Where π = 22/7 or 3.14, a and b are the radii of the base of the elliptical cylinder, and h is the height.

Elliptical Cylinder Formula can be used to Calculate Volume of a bag

Once again, I have prepared the below Backpack Volume Calculator based on the Elliptical Cylinder formula. All you need to do is enter the Length, Width & Height of your bag -- and voilà! The volume will be calculated for you automatically. Enjoy!

In order to check the accuracy of this new formula, we have run tests comparing both formulas, on 10 different backpacks from Osprey, Arc'teryx, Gregory, REI, Mystery Ranch and Deuter, and the results are as follows.

Based on our test, elliptic cylinder formula is a more accurate way of calculating backpack volume than traditional methods.

10 out of 10, the elliptic cylinder formula has generated results that are closer to the official volumes published by the manufacturers. This experiment suggests that V = π abh is more accurate than Length (L) X Width (W) X Height (H) = Volume when being used to measure similar hiking backpacks.


Method 3: The Most Accurate Way

This is the beads-filling method that we have used for many years as a bag factory, and it works very well. This method has taken Standard Test Method for Measurement of Backpack Capacity ASTM F2153 – 07 as reference, but we have adjusted a bit to fit our needs. Here are the steps:

1) First, you need lots of little balls or beans

We use plastic balls with 20mm diameter, but you can use anything available such as Ping Pong balls or dried beans. You need lots of them.

To use the beads-filling method to measure your backpack's volume, you will need lots of little balls or beans.

2) Fill the backpack using a measuring cup

Fill the backpack with balls/beans until it is completely full.

Fill the backpack with little balls to determine its volume.

Some would fill the main compartment only (as suggested by ASTM F2153), and others would also include the outside pockets as well. There isn't really a standard. In my opinion, I would include the outside pockets as well because they also contribute to storage capacity.

3) Just count how many cups of balls/beans you have filled

You can get the accurate volume of the backpack by checking the amount of balls/beans you have filled in.

We can calculate the volume of a backpack by counting how many liters of little balls it would take to fill up that space.

For example, if you are using a 1L measuring cup, and the backpack can take 20 cups of ball/beans, then the volume of the backpack is simply 20L. This is straight forward, right?

This method for measuring backpack capacity is not only accurate but also user-friendly, once you have all the necessary tools set up. I highly recommend it to all backpack manufacturers and factories. I know that Mystery Ranch uses a similar method to calculate its backpack volume. You can check out their website ( for details. By the way, Mystery Ranch does not consider areas that are not entirely enclosed by fabric—such as mesh pockets and water bottle holders.


So, these are the 3 ways to measure backpack volume. I hope you will find the information interesting and useful. These methods also work for other bag types, such as totes and messengers. However, the elliptic cylinder volume formula is probably best for backpacks specifically.

I hope you enjoy reading this article and find it helpful. Don't forget to share it with your friends and colleagues if you like it. Also, feel free to drop me a message below to let me know your thoughts!

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