A 40 x 30 x 20 cm bag fits under the seat on most airplanes. Ryanair designed its current free personal item size to this exact dimension so it fits under the seat in front of you on every aircraft in its fleet.
Underseat space varies by airline and seat row:
- Standard economy seat: around 40 x 30 x 20 cm underseat clearance. A 40 x 30 x 20 cm bag fits.
- Bulkhead and exit rows: no underseat storage. Bags must go in the overhead bin.
- Premium economy and business: usually more underseat space, sometimes 45 x 35 x 25 cm.
Measure the bag including wheels, handles, and external pockets. A bag that is 41 or 42 cm in any dimension will not fit under most economy seats.
See: luggage calculator and airline size limits.