The specific engine displacement required for a scooter to be street legal can vary depending on the country or region you are in. Different jurisdictions have their own regulations and requirements for vehicle classifications, including scooters.
In many countries, smaller scooters with engine displacements of 50cc or below are considered "moped-class" vehicles and can be operated with specific licensing requirements, such as a moped license or a lower minimum driving age. These smaller scooters are often designed for city commuting and have limited top speeds.
For scooters with higher engine displacements, typically ranging from 125cc to 300cc or more, they are classified as motorcycles and require a standard motorcycle license to operate. These larger scooters are capable of higher speeds and are designed for longer-distance riding and highway use.
It is important to consult the local traffic regulations and licensing authorities in your specific region to determine the exact requirements and restrictions for street legal scooters. They can provide the most accurate and up-to-date information on the engine displacement limits, licensing requirements, and any other specifications for legally operating a scooter on public roads.