Under Seat Cabin Bag: Sizes, Policies & Best Picks

Figuring out the exact dimensions of an under seat cabin bag can feel like decoding a secret airline language. With each carrier setting its own size limits—and enforcement varying from gate to gate—it’s easy to end up with a bag that’s just a few centimeters too big.

Typical underseat bag dimensions: 18 x 14 x 8 in (45 x 36 x 20 cm) ·
Ryanair free underseat allowance: 40 x 20 x 25 cm (including wheels and handles) ·
Budget airlines with similar underseat limits: EasyJet, Aer Lingus, Vueling, Wizz Air ·
Estimated weight of empty underseat bag: 1.0–1.8 kg ·
Baggage fee saved per flight: €15–€30

Five major airlines, one telling pattern: the allowed underseat size varies by as much as 12 cm in the longest dimension, yet budget carriers all cluster around 40–45 cm length.

What size bag fits under the seat on an airplane?

Standard underseat dimensions across major airlines

Most US airlines accept an under seat bag up to 18 x 14 x 8 inches (45 x 35 x 20 cm), according to Which? consumer group. Budget European carriers are tighter: Ryanair allows 40 x 20 x 25 cm (Ryanair official bag-sizer explainer), while EasyJet gives you 45 x 36 x 20 cm (Which? comparison). Antler’s luggage guide cautions that these figures include wheels, handles, and any protruding pockets.

How to measure your bag correctly

Lay your bag flat, measure the longest side (height), then width, then depth. Vagari Bags’ 2025 guide notes that the sizer bins at the gate are the ultimate judge: if your bag doesn’t slide in easily, it’s too big. Soft-sided bags can sometimes compress a centimeter or two; hard cases cannot.

Is a 40x20x25 bag allowed on Ryanair?

Ryanair official policy for free underseat bag

Yes, 40 x 20 x 25 cm is exactly Ryanair’s free underseat allowance for all passengers, as confirmed by Ryanair’s official bag-sizer video. The airline also states on its partner site that there is no weight limit for this small bag. Priority and Plus customers can bring a second cabin bag up to 55 x 40 x 20 cm with a 10 kg weight cap (Vagari Bags).

What qualifies as a 40x20x25 bag

The sizer at the gate will only accept a bag that fits completely inside, with no handles or straps sticking out. Cabinzero’s guide emphasizes that wheels and handles are included in the measurement, so a bag labeled “40 cm” may actually need to be 38 cm or less to fit the sizer.

How strict are Ryanair with under seat bags?

Enforcement at the gate vs. at check-in

Ryanair is known to enforce size checks primarily at the gate, not at check-in counters. Which? reports that the airline regularly uses sizer bins before boarding, and passengers whose bags don’t fit are charged a €20–€30 gate bag fee.

What happens if your bag is slightly too big

Even a 2 cm excess can be flagged, according to Cabinzero. However, discretion varies by airport. Vagari Bags notes that soft-sided bags are more likely to be allowed if they can be squeezed down.

Tips to avoid being charged

• Choose a soft-sided backpack or duffel bag that compresses easily.
• Remove items from outer pockets before approaching the sizer.
• Wear bulky clothing items instead of stuffing them into your bag.

What is the best underseat bag?

Top picks for Ryanair and budget airlines

The best underseat bags weigh under 1.5 kg, have a separate laptop compartment, and an expandable main section. Cabinzero recommends backpacks that are slightly under the max dimensions to account for the sizer tolerance. Antler’s guide praises hard-side mini-cases for protection but warns they are heavier and less forgiving.

• Soft-side backpacks (e.g., CabinZero 28L Military) – flexible, light (~0.8 kg)
• Hard-side underseat suitcases (e.g., Samsonite Lite-Align 40 cm) – durable but ~2.0 kg

Features to look for

A dedicated laptop sleeve, compression straps, and a water-resistant outer fabric are key. Vagari Bags highlights that a trolley sleeve is essential for attaching the bag to a larger suitcase when connecting flights.

What suitcase do flight attendants say not to use?

Reasons flight attendants advise against certain suitcases

Oversized hard-side suitcases with external handles or bulging wheels are the top offenders. According to anonymous flight attendant reports cited by Cabinzero, these bags cannot be compressed to fit under the seat, block foot space, and slow down boarding. Flight attendants recommend soft-sided duffels or compact backpacks for underseat-only travel.

Best alternatives for a stress-free flight

Instead of a hard case, choose a duffel bag with a padded laptop sleeve or a convertible backpack that meets 40 x 20 x 25 cm. Which? tests show that flexible bags are far more likely to pass gate checks without incident.

Four airlines, one clear contrast: free underseat allowances differ by up to 9 cm in width, which dramatically affects which bags work across multiple carriers.

Seven spec points, one pattern: weight and material flexibility matter more than exact dimensional compliance when dealing with budget airline sizers.

“Our free small personal bag must fit completely inside the sizer with no handles or straps sticking out. We measure including wheels and handles.”

— Ryanair spokesperson, official bag-sizer explainer

“We check about 20% of passengers at my airport, and two centimeters over the limit usually gets flagged. Soft-sided bags often slip through because they compress.”

— Anonymous gate agent, European hub (as told to Cabinzero)

“Hard-sided suitcases that don’t compress are the biggest headache for underseat storage. They often get pulled and checked at the gate, delaying the whole boarding process.”

— Anonymous flight attendant, reported by Which?

For the casual European traveler who flies Ryanair or EasyJet two to four times a year, the choice is clear: pick a soft-sided backpack or duffel under 1.2 kg that matches the strictest allowance (40 x 20 x 25 cm), or risk paying an extra €20–€30 per flight when the sizer says no.

Frequently asked questions