Backpack Size Guide For 2021 (How To Measure & Fit Properly)

Backpacks are an essential piece of gear. You use them for school, everyday life, and traveling, so getting the right backpack is essential. The most important feature of a backpack is the size, and you need to make sure you get a backpack that's the right dimensions for you.

Finding the right size backpack can be challenging, and there is a massive amount of choice on the market. This guide will give you all the information you need to know to understand the options and pick the right size backpack that meets your needs.

What Size Backpack Do I Need?

Several key factors will impact the size of backpack you need. You should take these into consideration before making your selection. 

User’s body type

Everyone is different, and you must consider your shape and size when selecting your backpack. If you don't, then, at best, it will be uncomfortable, but at worst, it can cause you an injury. The critical measurement here is your torso, and you can do this by following these steps:

  1. 1
    Lean your neck forward and look for the C7 cervical vertebra (this is the bony protrusion at the top of your spine, between your neck, and the slope of your shoulder). This is where your measurement will start.
  2. 2
    Move your hands to the top of your hip bones at your waist. Trace a circle around your body from here to find the bottom of your torso for the measurement.
  3. 3
    With your back straight, ask a friend to measure the distance between these two points. This is your torso length.

Well-known brands like Gregory and Osprey use this measurement and actually give their own guide on measuring your torso. If you have a brand in mind, it's worth checking to see if they have a particular method they recommend for measuring your torso just in case it impacts the size.

The other measurement that can be useful is your hip width because some of the weight will be distributed here. You can do this by running a measuring tape around the top of your hip bones and recording the length. Not all brands will have a waist measurement to select, so it might be worth checking first.

Weight Capacity

The weight capacity of a backpack will vary massively depending on the make, model, and size of the bag. You need to consider what you'll be using the backpack for and then look for a weight capacity that will meet that need.

The general rule is the larger the backpack, the higher the weight capacity, but there are some exceptions. The weight capacity is usually advertised clearly, so you should be able to find it easily enough when browsing.


Backpacks are true multi-functional tools, and we all use them slightly differently. If you're planning to use it in particular conditions, you will need to select a material that protects your belongings inside.

If you're going to use it while hiking or camping, you'll want to look for a tougher material and water resistance. You might also want a larger backpack with room for hydration packs.

Personal packing style and preferences

There's no hard and fast way to pack a backpack, and everyone approaches it slightly differently. You should consider this when selecting a backpack because more organized packers may only need a small backpack. Check out our tips and tricks to packing a backpack efficiently here.

Backpack Size Guide

How to Measure Backpack Sizes

Once you've determined the size of the backpack, you'll need to check out the options. Backpack manufacturers generally measure backpacks in one of two ways, but occasionally both metrics are provided:

Measuring by Volume

The volume of a backpack is literally how much space there is available in the backpack. This is most commonly provided in liters but sometimes can come in cubic inches. You can measure the volume of the backpack by calculating how much each individual compartment and pocket of the bag can store. This is then added together to give the total. It's worth noting that sometimes only the main compartment is used for volume.

Measuring by Actual Dimension

The dimensions are the height, length and width of the backpack. This gives you less of an idea of how much you can fit within it but makes it easier to work out how it will fit on your body and whether it matches your torso height. You can use the dimensions to work out the volume of the backpack if you need it.

Standard Backpack Sizes: Capacity Explained

If you're looking at different volumes, it can be challenging to know what it actually means. Here's a quick breakdown:

  • 0-10 LITERS
    This is a very small backpack which is used to carry the essentials. You won't be able to fit a lot in, and typically these are used by runners as hydration packs.
  • 10-20 LITERS
    These backpacks are the next size up, but they're still pretty small. They work well for day trips or commuting to and from the office and can fit some food, clothing, and other essentials.
  • 20-30 LITERS
    This is the most common size of backpack, and you'll see these in most stores. These will allow you to take everything with you for the day but wouldn't really work as an overnight bag. Typically this size would be used for school or college.
  • 30-40 LITERS
    This size backpack is perfect as an overnight or weekend bag. They typically have a number of small pockets, which allow you to separate your belongings and make it easier to find everything. This size backpack is perfect for an adventure over a couple of days and will allow you to carry some food and essentials but might not be able to accommodate any sleeping gear.
  • 40-50 LITERS
    We’re starting to get into the region of ‘big’ backpacks now with the 40-50 liter. These are great for camping and will have room for clothing, food, and other essentials for 5-6 days. You can even fit cooking gear and a sleeping bag in this backpack. This backpack would be too big for day-to-day use, but some may consider it too small for their adventures. If you're a serious camper, then this is the smallest backpack you should consider, but you may need a larger size.
  • 50-60 LITERS
    These backpacks offer more space and are perfect for serious campers. You can fit your food, clothing, supplies, and even your tent if needed. These backpacks are perfect for 1-2 people to go away for a few nights and typically handle a fair amount of weight.
  • 60-70 LITERS
    These backpacks are also well suited for long camping trips and can fit everything you need for up to 10 days. They will have many different secure compartments to store various items and allow you to fit some luxuries alongside the necessities.
  • 70-80+ LITERS
    A backpack this size is for a big adventure. This will be able to fit everything you need for longer expeditions and works well for those with families and young children who can't carry their own gear. High altitude climbers will typically use this size backpack.

Backpacks Average Size: According to Types and Uses

School Backpacks

School backpacks are essential, and you need to have the right size. Too small and you can't fit your books, too big and it won't fit in your locker. Typically, school backpacks should be 6-20 liters which will allow space for your books, stationery, and lunch. You may need something bigger for high school or college.

Suitcase backpack

Suitcase backpacks are a popular choice for frequent business travelers. They need to be large enough to fit documents and a change of clothes but small enough to fit in an overhead storage unit on an aircraft. You also want these backpacks to be comfortable and portable. Typically these are in the 25-40 liter range.

Hydration backpacks

Hydration backpacks are used by runners, hikers, and cyclists so they can stay hydrated while they move. These backpacks have a hydration bladder within them which allows you to store water in the backpack directly. A pipe is attached, allowing you to drink while running or moving. These backpacks need to be compact and lightweight and are typically 7-10 liters.

How To Measure A Backpack

Everyday backpacks

Everyday backpacks need to be able to handle whatever life throws at you. The size and shape of the backpack will depend on your typical day, but you'll want enough room for a jacket, some food, some water, and maybe some other essentials. Everyday backpacks should typically hold 15-35 liters.

Hiking backpacks

Hiking backpacks need to be larger so you can fit all your equipment in them. This could include food, drink, clothing, a sleeping bag, and a tent. Hiking backpacks are heavy-duty and more durable against the elements. Typically you would expect a capacity of 20-60 liters, depending on the exact nature of your adventure.

Compression backpacks

Compression backpacks are designed to make your trip more efficient. They can compress down and become even more compact, which is perfect if there's limited storage space. Compression backpacks are ideal for travelers who want to maximize capacity without taking up a lot of room. Typically they are 15-50 liters.

Tactical military backpacks

Tactical military backpacks are designed for military use and often have distinct camouflage coloring on the outside. They're heavy-duty, durable, and very resistant to damage even in harsh conditions. Tactical military backpacks need to fit a lot of things in and are typically 25-50 liters.

Carry on travel backpacks

Carry-on luggage has specific dimension requirements (typically 22" x 14" x9), and if you're a traveler, you need a backpack that meets these. If you're a frequent traveler, you may want to invest in a carry-on backpack, and these are typically 30-40 liters.

People Also Ask (FAQs)

What size of a backpack do I need for backpacking?

Typically, you want your backpack to be 20-35 liters. This will allow you to pack enough for the trip, but it won't weigh you down as you travel.

What size backpack do you need for mountaineering?

A 20-40 liter backpack is usually sufficient for mountaineering. It allows you to carry all the necessary items, including a first aid kit, map, and insulated clothing, without being too bulky to carry.

What size backpack do I need for 3 days?

For a 3-4 day trip, you should look for a 40-50 liter backpack, but this may vary depending on the activity you’ll be undertaking.

How do I know if my backpack is too small?

Generally, you will know if your backpack is too small because you can't fit your belongings in and it's uncomfortable. If there is too much room between your shoulders and the shoulder straps, it will also mean it's too small.

What size of a backpack do I need for a European trip?

If you're backpacking across Europe, then you should consider a carry-on travel backpack that will comfortably fit on the plane. These are usually 30-40 liters.


Backpacks are really useful. If you have the right backpack, it can make your life so much easier, and it's worth taking the time to find the best backpack for you. The most important factor is the size of the backpack because if you get this wrong, then it can just become a hindrance. Hopefully, this guide has given you everything you need, and you can now select the right size of backpack with confidence. 

  • Updated November 3, 2021