The most common measurements are around 55 × 40 × 20–25 cm, but in practice, airlines don’t measure to the millimeter.
The most important thing is that the suitcase fits properly in the overhead compartment and doesn’t stick out noticeably.

In our experience, well-designed and proportionate suitcases pass through without issues even if they slightly exceed those measurements.

Under normal circumstances, no.
Strict baggage checks usually focus on clearly oversized or rigid suitcases that don't fit the sizing gauges. A carry-on suitcase slightly larger but well-balanced and easy to handle will rarely cause issues.

That said, some low-cost carriers have strengthened baggage checks (there's even talk of staff incentives for spotting oversized luggage), so it’s best to travel thoughtfully: don’t push measurements using the brick method and avoid overpacking.

That’s why we recommend prioritizing real functionality and smart design, not just the numbers on a technical spec sheet.

Today, most travelers are opting for  hard-shell suitcases, and this makes perfect sense: materials have evolved, and rigid no longer has to mean heavy. Many modern hard-shell cases (especially  polypropylene and polycarbonate) offer an excellent balance between  weight, durability, and protection; ABS is often a fantastic quality-to-value choice.

Soft-shell suitcases still make perfect sense if your top priority is  flexibility  or you’re looking for a  specific ultra-lightweight model. But if you ask me as a store specialist: for carry-on luggage, for comfort and durability,  hard-shell suitcases are the safest bet for most travelers.

Important note:  both hard-shell and soft-shell suitcases  come with  warranties and access to replacement parts for years (wheels, handles, pull handles) depending on the manufacturer, which makes a huge difference compared to "no-service" purchases.

It depends on your type of travel:

• ABS: a great choice if you travel occasionally and want a quality-to-price ratio. 
• Polycarbonate: an excellent balanced option for those who travel more often; it is the most durable and long-lasting.
• Polypropylene: highly valued for its light weight and overall durability; a top-tier pick when you’re looking for an "all-purpose" suitcase. The quality-to-price ratio is unbeatable.

Expert summary: if you travel frequently, it’s worth opting for polycarbonate or polypropylene; if you travel once in a while, ABS may be more than sufficient.