Backpacks are very useful tools that allow us to carry our belongings without having to carry them around. They come in various shapes and sizes, depending on their purpose. 

Backpack size is important because it determines how much stuff you can fit inside. If you don’t know how to measure backpack dimensions, then you may end up purchasing the wrong sized one for your needs.

Whether you are buying a backpack for traveling, school, or hiking, we have the ultimate guide to help you understand the difference between backpack dimensions so you can choose the best one.

How To Measure Backpacks– Essential Measurements

Whatever type of backpack you buy, there are two main methods to use in order to figure out the backpack size. We explain these two methods of measuring backpacks below.

1. Actual Dimensions

The first way you can figure out the size of a hiking backpack is to measure its outside, inside, and compartments.

You simply need a ruler or a tape measure, whatever tool is at hand for you. Using a ruler or tape measure, measure the length, width, and height of the backpack. If you want to figure out the interior dimensions, then repeat the same steps to measure the interior compartments- done!

Once you have all of these measurements, you’ll know what fits in a particular backpack and what it’s best suited for.  

2. Height Measurement: Ensuring the Right Fit for Comfort

The height of a backpack is vital for comfort, especially if you’re carrying it for long periods. An ill-fitting backpack can cause back and shoulder strain. Measure from the base to the top, and consider your body size when choosing a backpack.

how to measure a backpack for fit

3. Width and Depth: Maximizing Storage Capacity

Width and depth determine how much you can carry. A wider backpack offers more space, but be mindful of it becoming too bulky. Depth is essential for fitting larger items comfortably.

4. Volume

Another way to work out the size of a backpack is by measuring the cubic volume of the backpack. You will most likely have seen online and in stores, that a number of backpacks references liters on the dimensions or product descriptions. Often referred to as capacity.

For example, you’ll see the capacity of an Osprey backpacking backpacks, since its volume is stitched onto the front. So with some packs and brands, you can tell if it’s 60 liters or other sizes pretty easily.  

Backpack Capacity size

Volume is the measurement used in reference to the fillable space inside the backpack. Most manufacturers calculate the volume of a backpack by adding up all useable space. Packs are advertised with a heavy focus on their volume (capacity).

All the usable storage space inside the bag is added together to find the volume. This can include small mesh pockets, water bottle pockets, and other interior and exterior pockets.

Volume= Length x Width x Height 

The simplest way to figure out the volume of a bag is to calculate, the length, width, and height using the method explained above.

Next, Multiply the Width by Height and by Width to get an approximate cubic volume of the backpack. Remember to calculate using centimeters, not inches to the liters listed on the pack.

While the volume of backpacks is usually given in liters, measurements given in cubic inches or centimeters, are more accurate. If you want to know the volume of a backpack without doing any math, then look at the product label to find this information.

Both of these methods will help you understand what backpack is best suited for what. 

5. Adjustable Features: Tailoring to Individual Needs

Many backpacks come with adjustable straps and compartments. Understanding how these adjustments affect the overall size and fit is crucial for a tailored experience.

Recommended Reading: 15 Best Camping Chairs – Don’t Sacrifice Comfort on the Trail

Standard Sizes Of Backpacks

Standard Sizes Of Backpacks

While backpacks vary in a range of shapes and sizes, they are all loosely based on standard sizes. The standard sizes of backpacks include both the volume and dimensions of a backpack. 

While the bag’s volume doesn’t indictate the exterior dimensions, by following the standard sizes, you can determine the backpack’s volume.

Below is an example of the most common standard sizes you can expect when looking for a backpack:

  • Smallest standard size: 8 Liter Backpack: 17” x 8” x 5”
  • 25 Liter Backpack: 21” x 11” x 6.5”
  • 30 Liter Backpack: 21” x 13.5” x 9.5”
  • 40 Liter Backpack: 21” x 14” x 9”
  • 50 Liter Backpack: 29.5” x 13” x 10”
  • 70 Liter Backpack: 28” x 14” x 12”
  • 110 Liter Backpack: 30” x 18.5” x 12.5”

As you can see there are only slight differences between the seven most common standard sizes. To find the best backpack for you, it is important you know your body proportions. Be honest about your physical abilities and strength too.

Do you have the ability to carry the backpack without causing injury or experiencing muscle fatigue, for a mile? Or can you go the distance with the Pacific Coast Trail or hike the Presidential Traverse? 

Before shopping for a backpack, it is worthwhile to measure the length of your back and find a daypack your back can support.  

Common Backpack Sizes And Uses For Hiking

Backpacks are a very important part of hiking gear and attire. Having the wrong one means you won’t be able to fit everything needed during a trip. Also, you will tire faster on the hike due to the additional weight from the incorrectly sized backpack. Worse yet,you can injuries while hiking that can easily avoided.

Below are the most popular sizes, used by hikers for specific types of hiking trips. 


Daypacks are typically used by hikers for short routes and trails, which can be completed between sunrise and sunset. These backpacks are specifically designed to carry all the essentials a hiker could need for a daylong hike. 

Daypacks have a capacity typically anywhere from 8 to 25 liters, usually quite short and compact, so they don’t weigh you down.

What’s more, daypacks are also often used by school and college students, to carry books and laptops around the school campus without injuring their backs.

Overnight Packs 

Overnight packs are perfect for anyone who intends to spend a night out under the stars after a hike. OThe backpacks are usually large enough to carry sleeping bags, tents, and other essential pieces of kit for a night out in the wilderness. 

These types of backpacking backpacks range from 30 to 50 liters. If you are looking to buy an overnight pack, then check for one ergonomically designed. Indeed, these can get quite heavy or uncomfortable due to the outdoor gear and various you carry.

Weekend Backpacks 

If you are planning a two-day hike and the goal is to go ultralight, then a weekend backpack should be big and lightweight. Certainly, you want one large enough to hold everything you could need, but also not be heavy. These backpacks tend to be longer, so it’s vital to check your back and torso measurements, to ensure you can support this backpack.

Weekend backpacks are usually between 30 and 70 liters. The larger capacity is the best, if you’re bringing camping cooking gear, backpacking meals, and sleep systems to create your sleeping setup. 

If you are planning a weekend hike with friends and plan on truck tent camping, then spread out the needed gear amongst the group. Each person should carry their own food and water. And then delegate one person to carry a specific type of outdoor gear, for example, cooking, sleeping, or general tools.

Multi-Day Backpacks

These are often the largest backpacks and are typically what you would see backpackers hauling around, for their thru-hikes or extended adventures. They can store a lot between interior and exterior pockets. In general, multi-day backpacking backpacks are ideal for when planning a longer hiking and camping trip.

As a result, these backpacks are sized between 50 and 110 liters. Since these backpacks can carry serious weight, make sure you are capable of carrying the load, before setting off on your adventure in the great outdoors.

Perhaps a dry run with a fully loaded bag for a couple of hours will give you a good idea if you can physically carry the bag.

Frequently Asked Questions FAQs

How much weight can a child carry in their backpack for hiking?

As a general guideline, a child’s backpack should weigh no more than 10-20% of their body weight. This range is recommended to prevent any strain or injury.
For example, if a child weighs 50 pounds, the backpack should ideally weigh between 5 to 10 pounds. It’s crucial to consider not just the weight but also how the backpack is packed and fitted. The heaviest items should be placed closest to the child’s back, and the backpack should fit snugly, with its bottom sitting at the child’s waist level, not hanging low.

Do hydration packs add to the overall size of a backpack?

Yes, hydration packs can add bulk and weight. Measure the hydration compartment and consider its full size when filled with water. This ensures the backpack remains manageable and balanced.

Final Thoughts

We hope that this piece has given you some important insight into the different sizes of backpacks that are available on the market.

When you are looking at either men’s or women’s hiking backpacks, its worthwhile going into a store to try them on to make sure that it is comfortable for you and your body size. 

Outdoor stores such as Patagonia, REI, and Columbia have a huge selection of backpacks, and once you have tried the one you want in-store you can look online for a better price.

Leave us a comment on how you fit a backpack

Join our Facebook Group – Outdoor Gear Reviews, Deals, Hacks & Advice- Backpacking, Hiking & Camping to get the latest reviews, deals, and discounts on backpacking, camping, and hiking gear. Share tips, and advice and to show our love, we also give monthly gear giveaways.