Which bag flies free on the plane? The biggest carry-on backpack (40x30x20) - now on sale

You book a cheap flight and then carry-on baggage suddenly turns out to cost €30 to €60 each way. Such a waste. The good news: almost every airline lets you bring one bag under the seat for free - as long as it fits within 40 x 30 x 20 cm. And since 2026 even Ryanair has increased that free size to 40 x 30 x 20 cm. So the question is: which bag flies free on the plane and still makes the most of that space? That is exactly what the Lundholm Underseater was made for - and it is temporarily on sale.

Two colors - now EUR 49.95

Timeless black or warm beige. While stocks last.

Underseater - Black

EUR 49.95 EUR 64.95

Underseater - Beige

EUR 49.95 EUR 64.95

Which bag flies free on the plane?

With most budget airlines you get one small piece of carry-on baggage for free as standard: the bag that fits under the seat in front of you. Larger cases in the overhead locker (cabin trolley) or checked baggage cost extra. At many airlines, that free "under the seat" bag has been given the same maximum size: 40 x 30 x 20 cm.

So if you would rather not pay extra, look for the largest possible bag that still fits just inside 40 x 30 x 20 cm. The Lundholm Underseater is designed for exactly that: at 40 x 30 x 16 cm it uses the full width and height, with a little room to spare on the depth.

Free under-seat size by airline (2026)

As of June 2026. Airlines sometimes adjust their rules and some (such as Vueling) apply a different size for the free item - always check the current rules for your own flight before you book. See the rules per airline at the bottom of this guide.

Why the Lundholm Underseater is so practical

This is not just another backpack with one extra pocket - it is genuinely designed to make your trip easier (and cheaper):

It opens like a suitcase. No digging in from the top: the Underseater folds all the way open with a suitcase-style layout, so you can pack neatly and find everything straight away. With 22 liters and compression straps on the sides you can pull it tight and compact.

Your laptop travels safely and separately. At the back there is a padded compartment for a 15.6 inch laptop - handy for working on the road, and easy to pull out at security.

Built-in TSA lock. The rear compartment closes with a TSA lock, so your belongings stay secure and airport security can open it without any damage. Ideal if the bag does have to go in the hold for once.

Waterproof. Fully waterproof material with waterproof zippers - your laptop and clothes stay dry, even in an unexpected downpour on the way to the gate.

Smartly organized. A separate pocket for your water bottle, several zippered and slip pockets, plus a security zipper against your back. Everything in its place, nothing lost.

It saves you money on every flight. Because it fits within the free under-seat size, you do not pay €30–€60 extra for carry-on baggage. After two flights the bag has already paid for itself.

The biggest carry-on without paying extra

The trick with the "biggest carry-on bag for the plane" is not the largest case out there, but the bag that makes the most of the free allowance. A bag of 40 x 30 x 16 cm uses almost all of the permitted 40 x 30 x 20 cm - with enough margin on the depth that it still slides under the seat when full. That way you travel with maximum capacity, without the risk of having to pay up at the gate after all.

Love, the Lundholm team