How to Measure Backpack Dimensions: A Simple Guide for All

Backpacks come in many shapes and sizes, and pictures are not always what they seem.

If you’re shopping for a new backpack for class, hiking, or simply to carry some things around, you may have a hard time visualizing just how big a backpack is going to be.

That’s because figuring out the sizing is not very intuitive until you have more experience with backpacks.

Learning how to measure backpack dimensions will help you to figure out if your bag will fit in a travel compartment, or if it’s going to be a good height for you to use. 

Knowing and understanding the size of your hiking backpack is a key purchasing factor, so you should get to know this technique today.

Methods of Measuring

Methods of Measuring

When it comes to backpacks of all types (basic, daypack, backpack, and travel backpack), there are two main ways of measuring the size of a backpack. The first method is to measure its volume, and the second is to measure its actual dimensions.

Check out our comprehensive list of the best hiking packs under $80!

Both measuring types can give you some useful insight about the bag and what it can be used for. Let’s talk about how to measure backpack dimensions in both ways, and why you might want to do so.

Measuring Actual Dimensions

One of the basic types of measurements that can help you to get an idea of the actual size and bulk of any hiking backpack is to measure the exterior dimensions of the bag.

Doing this is simple! All you need is a tape measure or a ruler. Use your chosen tool to find out the length, width, and height of the bag in question.

If you want to go a step farther, you can also measure the interior compartments of the bag in the same way. Gathering all of this specific information about your hiking backpack will help you figure out what you can fit inside of the bag with ease and what will simply be too large.

Measuring Volume

The other way that you can measure a backpack is to measure its volume. When you see a measurement rating such as 45L or 30L in reference to a hiking backpack, this measurement is talking about the volume of the bag. Volume is the total three-dimensional space that can be filled in a bag.

Check out the useful video below to learn more about backpack sizing.

When backpack manufacturing companies calculate volume, they typically add together all of the usable space from every single compartment in the bag.

Often, this even includes exterior pockets such as a mesh pocket for a water bottle. However, this is not a set standard to how the volume of a bag has to be measured.

If you are trying to measure the volume of a bag at home, the simplest way to do it is to multiply out the dimensions that you gathered in the “Measuring Dimensions” section above and then multiply the length by the width by the height of the bag to get a rough estimate of its volume.

Often, the volume of a backpack is expressed in liters. While measurements in cubic inches can be more accurate, using liters for volume is a rising standard in the backpack world that won’t go away any time soon.

Some Standard Sizes

Now that you have an understanding of both volume and exterior dimensions, let’s combine the two as best as we can.

While the volume of a bag cannot determine how large it will be on the outside due to the inconsistencies in measuring practices, we can generalize how large bags of a particular volume usually are.

  • 8L backpack: 17” x 8” x 5”
  • 25L backpack: 21” x 11” x 6.5”
  • 30L backpack: 21" x13.5" x 9.5"
  • 40L backpack: 21” x 14” x 9”
  • 50L backpack: 29.5" x 13" x 10"
  • 70L backpack: 28" x 14" x 12"
  • 110L backpack: ‎30” x 18.5” x 12.5”

The size of the backpack that you choose depends not only on the volume that it can carry but also the size of your body and the length of your back. Based on your measurements, you should aim to find a backpack that has similar measurements while still having ample space.

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Common Hiking Backpack Sizes and Uses

Now that we all have an understanding of how to measure backpack dimensions, let’s talk about the most common sizes of backpacks and what they are most often used for.


  • Range from eight to 25 liters
  • Perfect for short hikes
  • Only meant to carry daylong essentials

Overnight Packs

Weekend Backpacks

  • Range from 30 liters to 70 liters
  • Great for those who need a few more things on a weekend trip

Multi-Day Backpacks

  • Range from 50 to 110 liters
  • Huge bags for long journeys
  • Can carry a lot of things

Measure Carefully

No matter which bag you ultimately decide will be the right size for you, it is essential that you keep the sizing in mind. Pay attention to how the manufacturer did the sizing of the bag to make sure you got something authentic.

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Lily Safi - July 10, 2021

Excellent post to select a right size travel backpack.
Actually for me, backpack size depends on the travel duration.
You mention here some cool tips that will really help newbies to choose a right size travel backpack to make their trip more convenient.

    Asen - July 10, 2021

    Thanks Lily. I’m glad you find it helpful!

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