Introduction
Travelling with only a carry-on backpack changes everything.
No baggage claim queues. No lost luggage. No unexpected fees at the airport.
But choosing the right backpack size can be surprisingly difficult. Too small, and you'll struggle to fit everything you need. Too large, and you might end up paying extra to check it in.
The good news?
Once you understand the difference between personal items and carry-on luggage, finding the right backpack becomes much easier.
Step 1: Understand the Two Types of Carry-On
Most airlines divide cabin luggage into two categories:
Personal Item
This is the smaller bag that fits under the seat in front of you.
Depending on the airline, this usually means backpacks between 18L and 30L.
These are perfect for:
- Weekend trips
- Business travel
- Budget airlines
- Minimalist travellers
Carry-On Luggage
This is the larger bag that goes in the overhead compartment.
Most airlines allow bags up to approximately 40L-45L, typically around 56 x 36 x 23 cm.
These are better suited for:
- Longer trips
- Colder climates
- Travellers carrying extra equipment
Step 2: Check Your Airline's Rules
Not all airlines follow the same rules.
A backpack accepted by one airline might be too large for another, especially when flying with low-cost carriers.
Budget airlines tend to be stricter with dimensions and may use sizing frames at the gate to check compliance.
Before travelling, it's always worth checking your airline's latest baggage policy.
A two-minute check can save you an expensive surprise later.
Step 3: Choose the Right Capacity
18L–30L: The Sweet Spot for Most Trips
For city breaks, weekend escapes and short business trips, an 18L-30L backpack is often more than enough.
These sizes usually fit under the seat in front of you, allowing you to avoid overhead luggage fees altogether.
They also encourage smarter packing and make moving through airports significantly easier.
40L–45L: For Longer Adventures
If you're travelling for a week or more, or need extra clothing and equipment, a larger backpack may make more sense.
A 40L-45L backpack maximizes airline carry-on allowances while still avoiding checked luggage.
For many travellers, it's the largest size worth carrying comfortably.
Step 4: Soft Bags Have an Advantage
Rigid luggage offers protection, but flexibility matters when flying.
Soft backpacks can compress slightly when needed, making it easier to fit them into airline sizing frames or overhead compartments.
That flexibility can often be the difference between boarding normally and paying unexpected fees.
Step 5: Don't Forget Weight Limits
Size isn't the only restriction.
Many airlines also apply cabin weight limits, often between 7kg and 10kg.
A heavy backpack reduces how much you can actually pack.
Choosing lightweight materials becomes surprisingly important once every kilogram counts.
Step 6: Pack With Airport Security in Mind
If you're travelling with carry-on luggage only, airport security rules become much more important.
Liquids must comply with local regulations, and electronics should remain easily accessible during screening.
A well-organized backpack makes security checks faster and considerably less stressful.
Step 7: Why Expandable Backpacks Make Sense
Travel plans change.
A backpack that works for a short business trip may feel too small for a long weekend away.
That's why expandable backpacks have become increasingly popular among frequent travelers.
Being able to compress your bag for everyday use and expand it when extra space is needed gives you significantly more flexibility without needing multiple bags.
Our Nomad Backpack was designed with exactly this in mind.
Starting as a compact everyday backpack and expanding up to 45L, it adapts to everything from daily commuting to longer trips while remaining suitable for carry-on travel.
Frequently Asked Questions
Is 45L too big for carry-on travel?
Usually not. Most major airlines accept backpacks up to approximately 45L as overhead carry-on luggage, provided they remain within the airline's size limits.
What's the difference between a carry-on and a personal item?
A carry-on goes in the overhead compartment. A personal item fits under the seat in front of you and is usually significantly smaller.c
Is one-bag travel realistic?
Absolutely. Many travellers comfortably travel for weeks using only a carry-on backpack by packing strategically and choosing versatile clothing.
Are roll-top backpacks good for travel?
Yes. Roll-top designs offer flexibility, weather protection and adjustable capacity, making them particularly useful for carry-on-only travel.
Conclusion
Choosing the right backpack size can completely change your travel experience.
Understanding airline rules, planning around trip length and selecting a flexible bag helps you avoid unnecessary fees while making travel simpler and more enjoyable.
For many travellers, the ideal solution isn't choosing between a small backpack and a large one.
It's choosing a backpack that can do both.