The true velocity of the star is called the space velocity and tangential velocity is the part of a star's total velocity which is perpendicular to the line of sight. Given below is the rotational velocity of star formula which is based on the space velocity and tangential velocity. Take the square of space and tangential velocity and subtract these both. Then, taking the square root of the resultant value, you will get the rotational velocity of star.
Rotational velocity of star formula is defined as √(a2-b2). Also, you can navigate to the online calculator provided above for ease calculations.