PID controller for a wall following robot

[kieraon]

Currently I am facing some problems in programming my robot to follow the wall precisely. I am using two stepper motors interfacing with Atmega32 micro board. Each of the stepper motor is controlled by different timers thus it is possible to change their speeds. The issue here is that I am not able to implement PID controller due to the fact that the stepper motors need a definite number of steps to rotate, wherelse the output of the PID is velocity. How shall i convert the velocity to number of steps?

[waltr]

number of steps per unit time equals velocity.