Here goes:
If the dragon fades in and out while walking:
(Total # of Frames)/(Frames/Step) = # of Steps
If the dragon seperately fades in, walks, fades out, then:
(Total # of frames - fading frames)/(Frames/Step) = # of Steps
Also, this could be relevant:
(Horizontal Resolution)/(# of Steps) = (Horizontal pixels/Step)