Velocity is a physical vector quantity; both magnitude and direction are needed to define it. The scalar magnitude of velocity is called "speed", which is being measured in the SI units as meters per second (m/s) or as the SI base unit of (m⋅s^{−1}). Revolution per minute(RPM) is the measure of the frequency of rotation. Use this online top speed RPM calculator tool that determines the top velocity of the motor or engine given the diameter and revolutions per minute values.