Ever looked at a 25-liter backpack and wondered if it’s big enough for a weekend? Or questioned if a 40-liter duffel will hold your gym stuff and laptop? You’re not the only one. Bag sizes in liters aren’t taught, but everyone wishes they understood them.
Let’s get into everything you need to know about bag sizes, so you don’t have to guess anymore.
What Does Liter Capacity Mean?
When a bag is X liters, that’s the space inside – how much water it could hold.
But here’s the thing: you almost always get less space than they say. Pockets, zippers, and the bag itself take up room. In my experience, expect 10-20% less space than what’s listed.
Liter Capacity: The Reality
- A 20-liter bag holds about 20 one-liter water bottles.
- But bottles are round and easy to pack. Your laptop and jacket aren’t.
- Oddly shaped items waste space.
- The bag’s design (pockets, build) changes how much you can fit.
I learned this when my 30-liter backpack couldn’t hold what my friend’s 25-liter pack could. Design is as important as size.
Backpack Sizes: The Full Story
Daypacks and School Backpacks (10-35 Liters)
10-15 Liters: The Simple Choice
Great for light trips or when you only need a few things. I use a 12-liter pack for quick store trips or walks. It holds a water bottle, snacks, a phone charger, and a light jacket.
What it actually holds: Phone, wallet, keys, small water bottle, snack, light jacket
15-25 Liters: The Everyday Bag
This is good for most daily stuff. My 22-liter work backpack has been my go-to for three years. It holds my laptop, lunch, notebooks, and other work items.
What it actually holds: 13-15 laptop, chargers, papers, lunch, water bottle, small umbrella, gym clothes (if packed smart)
25-35 Liters: The One Who Does It All
Good for long days, students with a lot of books, or those who like options. I use a 30-liter pack for all-day events where I need materials, tech, and free stuff I get.
What it actually holds: Big laptop, many notebooks, full lunch, change of clothes, tech stuff, first aid kit, extra layer
Hiking and Travel Backpacks (35-80+ Liters)
35-45 Liters: The Weekend Trip
Good for 2-3 day trips or hikes where you need extra things. My 40-liter pack has worked for camping trips and photography trips in different weather.
What it actually holds: Sleeping bag, light tent, 2-3 days of food, cooking stuff, extra clothes, safety gear
45-60 Liters: The Standard for Hiking
The most common size for serious hikers going on 4-7 day trips. It gives you room for your stuff without being too much. I’ve used a 55-liter pack for five-day trips and it was fine.
What it actually holds: Full hiking gear for up to a week, including tent, sleeping stuff, cooking gear, food, clothes, and safety gear
60-80+ Liters: The Big Trip
For long trips, winter camping, or carrying group gear. I only use my 70-liter pack for winter trips (winter gear takes up a lot of space) or when I’m carrying things for a group.
What it actually holds: Gear for long trips, winter camping gear, group cooking gear, emergency supplies, or stuff for 10+ day trips
Sling Bag Sizes: Small and Easy
Sling bags are popular because they’re easy to get to and good for cities without being a full backpack.
3-8 Liters: The City Bag
These small slings are good for walking around cities. My 6-liter sling bag is good for concerts, festivals, or days when I want to carry a few things.
What it actually holds: Phone, wallet, keys, earbuds, small snacks, maybe a small camera
8-15 Liters: The Day Trip Bag
These can hold more daily things. I use a 12-liter sling for taking photos when I need camera gear but want to move easily.
What it actually holds: Camera with extra lens, phone, wallet, snacks, small water bottle, light jacket
15-20 Liters: The Biggest Sling
This is almost a small backpack but with one strap. These are good for going to work or traveling when you need some things but want them easy to get to.
What it actually holds: Small laptop or tablet, papers, travel things, snacks, water bottle, light jacket
Tote Bag Sizes: Stylish and Easy
Tote bags might seem simple, but size matters, especially for work, shopping, or travel.
10-20 Liters: The Normal Tote
Good for everyday things with style. Most totes are this size. My leather work tote (about 18 liters) holds my office stuff while looking professional.
What it actually holds: Laptop, notebook, lunch, wallet, makeup bag, phone charger, small umbrella
20-35 Liters: The Big Tote
These bigger totes are good for shopping, beach days, or when you need to carry more. I have a 30-liter canvas tote that’s good for farmers market trips or beach days.
What it actually holds: Beach things, groceries for a few days, many books, change of clothes, picnic things
35+ Liters: The Weekend Tote
These totes are real travel bags. I’ve used a 40-liter leather tote for weekend trips when I wanted something nicer than a duffel.
What it actually holds: Weekend clothes, toiletries, shoes, laptop, books, travel papers, souvenirs
Duffel Bag Sizes: Useful Bags
Duffel bags are useful for the gym, travel, sports, and more.
20-35 Liters: The Gym Bag
This is the normal gym bag size. My 30-liter duffel has been my gym bag for years. It holds workout clothes, shoes, toiletries, and other gym stuff.
What it actually holds: Gym clothes, shoes, towel, toiletries, water bottle, protein shaker, maybe change of work clothes
35-50 Liters: The Weekend Bag
Good for short trips or when you need more space. I use a 45-liter duffel for weekend trips. It’s easier to pack than a suitcase but stronger than a soft bag.
What it actually holds: 2-3 days of clothes, shoes, toiletries, electronics, books, travel papers, room for souvenirs
50-75 Liters: The Travel Duffel
These compete with suitcases but are more flexible. My 65-liter travel duffel has been on trips where I needed a lot of stuff but wanted a soft bag.
What it actually holds: Week of clothes, many shoes, full toiletry bag, electronics, books, travel gear, shopping
75+ Liters: The Big Mover
For carrying a lot of gear, sports stuff, or for long trips. I’ve borrowed 90-liter duffels for moving and long trips.
What it actually holds: Camping gear for some people, sports gear, many clothes, big things like sleeping bags and tents
Special Bag Sizes: Beyond the Basics
Camera Bags (5-25 Liters)
Camera gear is heavy and oddly shaped, so size is different. A 15-liter camera backpack might hold more camera stuff than a 30-liter regular backpack.
Laptop Bags (10-30 Liters)
These focus on protection instead of space. A good 20-liter laptop bag can often carry more everyday items than a basic 25-liter backpack.
Diaper Bags (20-40 Liters)
Parents need space, and diaper bags give it. Even small diaper bags are often 25+ liters because baby stuff is big.
Shopping Bags (15-50 Liters)
Shopping bags vary a lot, but most good grocery bags are 20-30 liters. My favorite shopping bag is 28 liters and handles a lot of groceries.
How to Pick the Right Size
After testing many bags, here’s how I decide:
Start with What You’ll Use It For
- Going to work: 15-25 liters is normal
- Weekend trips: 35-50 liters for most
- Long trips: 50-70 liters unless you pack light
- Gym/sports: 25-35 liters for most
Think About How You Pack
- Pack light: Pick 20-30% less space than you think
- Pack for everything: Add 25-40% to your guess
- Different seasons: Winter gear takes 50-100% more space than summer gear
Think About the Bag’s Design
- Good bags with pockets are easier to pack
- Bags with straps on the outside give you more space
- Bags that get bigger give you options but can make you pack too much
Test with Your Things
If you can, pack your things in the bag before buying. Reviews often say what fits, which helps.
Common Size Mistakes
Mistake #1: Bigger is Better
I used to think I needed a big bag. This made me pack too much. Picking the right size makes things better.
Mistake #2: Ignoring Shape
A 30-liter sling bag isn’t the same as a 30-liter backpack. Shape matters a lot.
Mistake #3: Not Thinking About Squishing
Some things squish (clothes), but others don’t (laptops, books). Knowing how your things pack helps.
Mistake #4: Wrong Season
Summer and winter gear need different space. Many people pick bag sizes based on one season.
Mistake #5: Not Thinking About Pockets
A smaller bag with pockets can be better than a bigger bag without them. Pockets matter.
Liter Size: What It Means
Here’s what liter size means in real life:
10 Liters = 2.6 Gallons
- About the size of a cereal box
- About 8-10 water bottles
- As much as a small grocery bag
25 Liters = 6.6 Gallons
- Size of a moving box
- About 20 water bottles
- As much as a full grocery bag
50 Liters = 13.2 Gallons
- Size of a big container
- About 40 water bottles
- As much as many grocery bags
Bag Care
Taking care of your bag helps it last and stay in shape:
Don’t Overstuff: Too much stuff hurts the bag and zippers.
Store It Right: Keep bags in shape to keep space inside.
Clean It: Dirt can take up space, especially in corners.
Zippers: Good zippers help you use all the space.
The Future of Bags
Mix and Match: More bags have parts you can take out to change the space.
Squish Tech: New materials let bags get big or small.
Smart Pockets: Better pockets mean you can use space better.
Making Your Choice
Picking the right size means knowing what you need. Here’s my advice:
First Time: Start with less space. You can always get bigger, but starting too big makes you pack too much.
For Things You Do: See what others use for the same things. Forums and reviews help.
For Everything: Pick a bigger bag with good pockets instead of many bags.
Long Lasting: Pick quality over size. A good 25-liter bag is better than a cheap 35-liter bag.
Last Words
The perfect size depends on you. It depends on your life, how you pack, and what you need.
The key is knowing what those liter numbers mean. A 30-liter backpack might be good for weekends but bad for work, or the other way around.
Don’t try to find one bag for everything. Pick bags with the right size for what you need them for. Your work bag doesn’t need to be a camping backpack, and your weekend bag doesn’t need to be a gym bag.
The best bag size holds what you need without making you pack things you don’t.
Ready to find your perfect bag size? Think about what you carry, add a little extra, and pick quality. Your back will like it.
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Note: Bag sizes can change between brands and types. This is just a guide based on what’s normal. Always check the bag’s details and try it with your stuff if you can before buying.
