The appropriate engine size (measured in cubic centimeters or cc) for commuting on a highway can vary depending on several factors, including the type of motorcycle, the desired speed, and personal preferences. Generally, motorcycles with engine sizes between 250cc and 500cc are considered suitable for highway commuting. These motorcycles provide enough power and torque to maintain highway speeds comfortably and handle typical commuting demands. However, some riders may prefer larger engines for more power and overtaking capabilities, while others may opt for smaller engines for fuel efficiency and ease of maneuverability in traffic. Ultimately, it is important to consider your specific needs and preferences when choosing a motorcycle for highway commuting.