Backpack Size Guide: What You Should Know

Buying a backpack online can be difficult. Of course, you know the backpack size you need, but it can be hard to tell if the pack will be too big or too small without actually seeing it in front of you.

To help make your decision easier, we have created a visual backpack size guide. That will show you which backpack sizes are available, what each backpack fits, and how much they hold.

In this blog post, we will discuss:

-How many liters do different sized backpacks typically fit?

-What is the difference between an 18L and 50L backpack?

-Why should I buy a backpack with an additional chest strap?

Backpack capacity is typically measured in cubic inches (in³) or liters (L).

For simplicity, we like to distinguish backpacks into three distinct categories: small, medium, and large.

  • Small: Backpacks with a capacity of fewer than 19 liters
  • Medium: Backpacks with a capacity of (20-29L)
  • Large: Backpacks with a capacity of (30-39L)

Exception: BACKPACKS OVER 40L

Backpacks larger than 40 liters are best utilized for traveling, hiking, or backpacking when you need to carry multiple days’ worth of gear.

For the following sections, I’ll go through each one in detail.

Small Backpacks (Under 19L)

Backpacks under 19 liters are best used for:

  • Essential daily carry (keys, water bottle, sunglasses, and other small items
  • Day hikes and short backpacking trips
  • Tech carry (laptop, tablet, and accessories)

What Fits Inside A 13L Backpack?

  • Up to 13″ laptop
  • Water bottle and sunglasses
  • Small tablet or e-reader
  • Sweater
  • Large headphones

What Fits Inside A 16L Backpack?

  • 13″ MacBook pro
  • Tablet
  • Water bottle and sunglasses
  • Headphones, sweater, small clothing items (tank-top)

Who needs a Small Backpack?

Backpacks that weigh less than 19 pounds are classified as “essentials only backpacks.”

It implies that you’ll have a very restricted carrying capacity, owing to the absence of external pockets. 

Therefore, we suggest small backpacks under 19 liters. That one is good for anybody who requires a simple work backpack for their laptop, water bottle, and food. Alternatively, it is a secondary personal item bag for air travel.

Smaller backpacks are ideal for anyone who wants to bring a laptop, tablet, adapters, and cables with them on their travels without having to carry around too much extra stuff.

Medium Backpacks (20-29L)

Backpacks between 20 and 29 liters are generally the most versatile backpack size.

You can use them:

  • Daily carry (keys, water bottle, sunglasses, and other smaller items)
  • Traveling – a couple of changes of clothes, toiletries, and other travel essentials
  • Day hikes – snacks, jacket, water bottle
  • Overnight trips – clothes for two days & gear, tent, sleeping bag & pad
  • Tech carries (laptop and tablet).
  • School and college (laptop, multiple books, and notebooks)

What Fits Inside A 20L Backpack?

  • 13″ MacBook pro
  • Tablet
  • Sunglasses, water bottle, and wallet
  • Clothing items (tank-top), jacket, snacks
  • Headphones and charger cables

What Fits Inside A 25L Backpack?

A 25L backpack fits most daily carry items but becomes more restrictive as you pack it.

  • 15″ MacBook Pro
  • Tablet
  • Water bottle
  • Jacket, snacks, and a few delicate clothing items – sweater, pants.

What Fits Inside A 28L Backpack?

28L backpacks are versatile enough to fit most daily carry items but become more restrictive as you pack them.

  • 17″ MacBook Pro
  • Tablet and a few books or notebooks.
  • Water bottle, snacks, and light clothing items – pants, tank-top.

Who needs a Medium Backpack?

Backpacks that weigh less than 29 pounds are classified as “travel backpacks.”

It implies a versatile carrying capacity, with external pockets for more accessible organization. Therefore, we suggest medium backpacks between 20 and 29 liters for anyone looking to travel, except for long-distance travelers who want something more significant.

Large Backpacks (30-39L)

Backpacks between 30 and 39 liters are good for:

  • Multi-day trips – clothes, gear
  • Tech carry (laptop & tablet)

What Fits Inside A 32L Backpack?

  • 17″ MacBook Pro
  • Tablet and a few books or notebooks.
  • Water bottle, snacks, and light clothing items – pants, tank-top.

What Fits Inside A 35L Backpack?

  • 17″ MacBook Pro
  • Tablet and a few books or notebooks.
  • Water bottle, snacks, and light clothing items – pants, tank-top.

Who needs a Large Backpack?

Backpacks with a capacity of more than 30 liters are overkill for most people who require only an everyday carry bag for essential goods.

These backpacks are also ideal for adults who need to transport their work things and a change of clothing and shoes while working out.

It’s also important to remember that backpacks with a capacity of over 30 liters are considerably more enormous in scale, making them difficult for small people to find. In addition, poorly constructed shoulder straps and back panels might make a backpack feel unpleasant on smaller bodies.

It pays to get a pack with a female fit to help accommodate slim shoulders and shorter torsos if you’re small.

Torso Length/Sizing

Torso length is the distance between your iliac crest (hip bones) and C-spine.

Again, you’ll need a buddy to help you out to determine this measurement.

Here’s what you do:

  1. Stand up straight with your back against a wall, and have your buddy place one end of a yardstick at your iliac crest and measure to the C-spine.
  2. Repeat this process on both sides.
  3. If the measurements are equal, you have an average torso length.
  4. You can also measure your torso with a flexible tape measure by placing one end at the C-spine and measuring down to the iliac crest.
  5. Remember that you can always size up if a backpack feels too small, but you cannot go one size smaller because of size limitations. No matter your torso length, we recommend choosing a bag with adjustable shoulder straps, so it’s easy to adjust the fit as needed for comfort.

How To Determine If A Pack Is Good For Your Torso Length

Backpack manufacturers use a sizing system based on torso length.

It’s essential to examine the sizing system and its relation to your torso before purchasing a backpack online. Then you’ll be able to determine if a pack will fit you well.

The sizing system typically goes like this:

Small – 15-17 inches/38-43 cm

Medium – 18 inches/46cm

Large – 19+ in./48+cm.

It’s important to note that companies use different sizing systems to describe their backpacks.

How To Determine The Number Of Straps

As we mentioned before, backpacks with an over 30 liters capacity are likely to have a pair of shoulder straps.

The number of shoulder straps can help you determine if the backpack is suitable for your height and torso length.

A two-strap system will feel more natural on smaller bodies because there’s less weight pulling down from the top of the backpack.

A one-strap system is suitable for people with average height but can feel a bit uncomfortable on petite builds.

Once you get more than 40 liters of capacity in your backpack, it will typically come with a detachable daypack that has a single strap and waist belt.

Detachable packs are great because they allow you to remove and carry them separately.

How To Determine The Right Fit 

Your backpack must fit you well, so it feels comfortable, even when complete.

When zipping up a backpack with an over-sized capacity, we encourage you to try out these simple tests:

Make sure shoulder straps fit comfortably and securely.

The shoulder straps should be able to sit flat on your shoulders, with no gaps between the fabric and torso.

When you tighten down the strap system, it feels secure without feeling tight or restricting the movement of arms or shoulders.

Adjustable sternum strap adds stability during fast hikes by keeping the chest plate stable.

The sternum strap must sit flat on your chest, just below the collarbone.

If you have a more petite build, this part of the shoulder straps might feel too big for small chests. It is not necessarily an issue with sizing but rather the design of specific backpacks.

When zipping up a backpack, ensure no gaps between the pack and body around the hips or ribs to ensure maximum comfort when carrying heavy loads for long periods.

To check if the waist belt fits appropriately, slide it into a place where it feels most comfortable, then tighten down any protruding buckles until they’re flush with fabric (using pliers can help with stubborn buckles)

You shouldn’t be able to fit more than your fist between the waist belt and your body.

Once you’ve worn your backpack for a little bit, check if there are any pressure points where it feels uncomfortable or painful to carry. If this is the case, consider adjusting shoulder strap placement by tightening down one side at a time until the pack sits more comfortably on your back. 

How To Determine Pack Capacity 

Pack capacity refers to how much space is available inside the main compartment (not including pockets). It can be confusing because manufacturers might use different measurements such as liters, cubits, etc.

Here are some tips: When comparing packs with 30-40L capacities, look at the main compartment’s height, width, and depth. Compare backpacks with 40-50L capacity by looking at volume or cubic inches (length x width x height).

If you want to compare packs with 50+ liter capacities, see if they come in different sizes (S/M/L) to ensure it’s not too big for your body type.

If the backpack is unisex, it might be good to look into smaller size options. Even men can benefit from using a pack that feels more comfortable on their backs than an oversized one.

When shopping online, consider checking out customer reviews before purchasing any high-volume backpack. Since it’s hard to tell how well this kind of backpack fits without wearing them first.

Think about the types of activities you will use this backpack for and how often. It can help narrow down or eliminate options that aren’t suitable to your needs and lifestyle (for example: if you’re a cyclist, steer clear from backpacks with bulky waist belts).

Now that we’ve gone over standard sizes, it’s time to find out what makes the best fitting backpack.

Here are our top picks when it comes to finding the perfect fit.

Our favorite is Osprey Levity 45. Even though it’s designed as an ultralight pack, its design has upped the game in terms of ergonomics. It’s super comfortable due to its lightweight fabric and flexible mesh, which allows it to conform to your body without adding unnecessary bulk.

Another excellent pack is TERRA PEAK Adjustable Hiking Backpack. Its customizable fit feature makes this backpack highly versatile for different adventure activities and all-day comfortability. You can adjust shoulder strap length and the height of the sternum straps depending on what feels best for you.

The hip belt also has a removable pad, so if you want total freedom from any extra weight, take off the waist buckle and leave only hip pads behind!

If you’re wondering about other great options, check out our list below:

Final Thoughts

I hope the backpack size guide has given you a better sense of backpack capacity and backpack sizing. If you have any questions or concerns, please leave me a comment below!

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Z Hashan

Z Hashan

I’m Z Hashan, an entrepreneur, but more importantly (well, to me at least), a traveler.

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