Carry less, better
Underseat Bag Size: The Centimetres That Matter
There is no single underseat size. Ryanair is 40 × 25 × 20cm. Many others sit near 45 × 35 × 20cm. Soft 18–22 litres, empty 0.7–1.2kg.
Updated 27 Aug 2026 · 6 min read · underseat bag size
Depth is the fight
Under the seat you have a cave that is short, wide, and not very deep. A bag that is 25cm deep will hit the rail or the life-vest box. 18–20cm packed depth is the useful band. Height of 35–45cm depends on the carrier; Ryanair’s 40cm height is the tight one in Europe.
Wheels and a telescoping handle steal 3–5cm and add 1kg. That is why underseat spinners are a bad joke. A soft pack from the personal-item backpack list is the shape that wins.
Numbers to actually pack to
Print the centimetres on a paper template and pack on it once. Softer bags can bulge past the tape and still slide in; leather briefcases cannot.
| Rule of thumb | cm | Litres (soft) |
|---|---|---|
| Ryanair small bag | 40 × 25 × 20 | 18–20L |
| Common US personal item | 43 × 33 × 20 | 20–22L |
| Generous underseat | 45 × 35 × 20 | 22–25L if compressible |
| Not underseat | 55 × 35 × 25 | That is cabin / carry-on |
Weight, laptops, weekenders
Empty 0.7–1.2kg. A 2kg empty “underseat” plus a 1.4kg laptop is most of a cheap-carrier weight limit before socks. A 13-inch sometimes fits the Ryanair box; a 16-inch belongs in a paid cabin bag.
A weekender only qualifies if it compresses into these centimetres. Most 40-litre canvas weekenders are 50 × 30 × 25cm stuffed — a carry-on. For Europe trip context, the 35–40 litre pack in the Europe backpack guide is the cabin bag, not the underseat bag. You may want both.
Questions, answered
- Is 40 × 25 × 20cm the same as 20 litres?
- 40 × 25 × 20cm is 20 litres of rectangle. Real bags have curves and pockets, so a labelled 20L may be taller. Believe the centimetres.
- Do airlines measure packed or empty?
- Packed, at the gate, in a metal box. Pack to the box, not to the product page.
- Can I put a personal item in the overhead?
- Sometimes, until the crew needs the space. Design the bag to live under the seat so you are not the person standing in the aisle.
