Bag Size Guide
Carry-On Bag Sizes Explained
Last updated: April 2026
Carry-on bag size is measured in liters, but liters alone don't tell you if a bag fits your airline. Dimensions, shape, and how you pack all matter. This page explains how to choose the right carry-on size by comparing liters to real-world dimensions and airline limits.
Overview
How Bag Size Actually Works
Liters measure internal capacity — not outer dimensions. A 40L bag from one brand can have completely different external dimensions than a 40L from another. Airline fit depends on external shape when packed, not the number on the tag.
Bag design also changes usable space. Dead space from bag shape, packing gaps, and rigid items reduces effective capacity by roughly 15%. A 35L bag holds about 30L of packed gear in practice. And the same liter size can behave very differently depending on whether you're flying Southwest (generous box) or Ryanair (strict box).
Not sure how liters translate to airline size? See our carry-on size in liters guide.
Bag sizes
Bag Sizes from 25L to 45L
Personal item / compact carry-on
25L
Best for: 1–3 day trips, light packers, warm weather
Fits under most airline seats as a personal item. Good for weekend trips with minimal gear. A laptop and extra shoes eat a large percentage of the bag at this size — add either and you're close to full. On budget airlines, this may be the only bag you get without paying extra.
Minimalist carry-on
30L
Best for: 3–5 day trips, light to standard packers
The sweet spot between personal item and full carry-on. Handles a long weekend or a light week-long trip. Room for a laptop on shorter trips without maxing out the bag. On budget airlines with strict limits, this is close to the overhead size ceiling.
Standard carry-on sweet spot
35L
Best for: 5–7 day trips, standard packers
Fits most trips up to a week without much compromise. Room for a laptop and basic extras. Sits comfortably within U.S. airline limits. Approaching the edge on stricter European carriers — bag shape starts to matter more here.
Extended carry-on travel
40L
Best for: 7–10 day trips, standard to heavy packers
Near the carry-on ceiling for most airlines. Handles a full week for most packers or 10 days with laundry access. Bag shape is critical at this size — soft-sided bags compress into sizers; rigid or boxy designs may not. On stricter European budget airlines, a 40L bag is often close to the limit and may exceed limits depending on shape and packed depth.
Upper-end carry-on / stricter airline risk
45L
Best for: 7+ day trips, heavy packers, cold weather
Near the upper carry-on limit on many airlines, and over the practical limit on stricter carriers. Can work on Southwest and some U.S. carriers if the bag compresses well, but risks gate-checking on stricter airlines. Often the tipping point where checking a bag becomes the better option.
Size vs trip length
Which Bag Size for Which Trip Length
3-day trip
15–25L
Personal item or small carry-on
5-day trip
20–35L
Flexible carry-on range
7-day trip
30–45L
Near carry-on limits
10-day trip
35–50L+
Carry-on vs checked decision
These ranges assume standard packers in mild weather. The relationship isn't linear — trip length increases clothing volume, but toiletries, electronics, and shoes stay constant. Laundry access flattens the curve by letting you re-wear clothing. Climate and bulky items shift the whole range up.
For detailed packing lists and a calculator for each trip length:
3-day packing guide →
5-day packing guide →
7-day packing guide →
10-day packing guide →
For destination-specific packing advice:
Europe packing guide →
Cruise packing guide →
Alaska cruise packing guide →
Placement thresholds
Personal Item, Carry-On, or Checked Bag
Personal item
15–25L
Under the seat, free on most fares
Small carry-on
25–35L
Overhead bin, fits easily
Full carry-on
35–45L
Overhead bin, airline-sensitive
Checked bag
45L+
Usually beyond standard carry-on range
These are typical thresholds, not hard rules. A well-designed 45L soft bag can fit in an overhead bin on Southwest. A rigid 35L might not fit on Ryanair. Packed shape, bag design, and airline enforcement all shift the boundaries. Use the airline-specific pages for exact answers.
Constraints
What Pushes You Up a Bag Size
- Cold weather — insulation layers add 10–15L regardless of trip length
- Extra shoes — each pair adds 5–7L of rigid, awkward volume that doesn't compress
- Laptop or tablet — adds 3–4L of rigid volume that can't be packed around
- Bulky layers — a heavy jacket or fleece takes more space than 2–3 days of clothing
- Heavy packing style — heavy packers use roughly twice the volume of ultralight packers for the same trip
- No laundry access — forces you to pack for every day instead of 4–5 days with re-wear
How to use
How to Use This Page
Start by choosing the bag size closest to what you own or are considering. Each size card above links to airline-specific fit pages where you can check whether that bag works on your airline with your packing setup.
If you're not sure what size you need, check the trip-length section above or start with a packing guide — the calculator will tell you how much volume your setup actually requires. Then come back here to find the right bag size and check airline fit.
Bottom Line
- Liters are helpful but incomplete — packed dimensions determine airline fit, not the number on the tag
- 35L is often the strongest carry-on middle ground for most trips and airlines
- 25L can be personal-item territory — good for short trips, borderline for anything longer
- 45L is airline-sensitive — it works on some carriers and gets gate-checked on others
- Use the airline-specific fit pages to check your exact bag, not just generic size advice
Notes
About Bag Volume Ratings
Bag volume in liters is a manufacturer rating and isn't standardized. Two bags rated at 35L may differ by several liters in actual usable space. Bag design matters — top-loading backpacks pack differently than clamshell designs, and rigid frames reduce usable space more than soft panels.
The calculator on each airline fit page accounts for this using a 15% dead-space factor and real packing measurements. Packed external dimensions are what determine airline fit — not the bag's internal volume rating. The volume ratings on this page are typical for travel backpacks.
How This Information Is Built
This page is based on aggregated airline policies, real-world packing constraints, and typical travel scenarios.
This content reflects real-world packing scenarios and typical airline policies. Airline enforcement may vary based on aircraft, route, and boarding conditions.
