To comfortably fit 23kg (the standard weight limit for most international economy flights) without overstuffing the bag or exceeding airline size limits, a "Large" or "Medium-Large" suitcase (typically 24 to 27 inches/60-70cm in height) is the most efficient choice. A standard "Large" suitcase usually has a volume of 75 to 95 liters. If you use a massive "Extra-Large" suitcase (30 inches+), it is very easy to accidentally pack over 30kg, which will result in heavy overweight fees at the counter. Conversely, a "Medium" bag (22-24 inches) can fit 23kg, but you would need to pack very dense items (like shoes and books) and it might be difficult to close. When choosing a bag for 23kg, consider the "tare weight"—modern hardside polycarbonate bags are much lighter than older fabric ones, giving you more of that 23kg allowance for your actual belongings. It is also vital to ensure the bag’s Total Linear Dimensions (Length + Width + Height) do not exceed 158cm (62 inches), which is the maximum size allowed by carriers like Delta and Lufthansa. Using a digital luggage scale before you leave for the airport is the only way to be 100% sure you have maximized your 23kg without crossing into the "overweight" territory.