Determine where you want your finished height to be, ie., do you want stairs from your ground floor to your first floor? If your first floor is say 2650mm above your ground floor, then you would take 2650 and divide by the height you would like your steps to be. If you were to make this 180mm for example this tells you you will need 14.7222222 steps. Round this off to 15 and you they will need to be 176.66 , round this off to 14 and they will need to be 189.26. Which one of these fits in better with your local government ordinances with regard to rise and going of a stair. What look do you want to have? low and long, or short and high.