How many steps you have depends on the rise and run of the stair way (how high it is, how long the base of it is) and there are a number of calculators online that can give you the answer if you give the measurements. Stringers are what supports stairs, so you would find these calculators under the topic "how to cut stringers" or "how to lay out stringers".... like this one:
The number of steps to a flight of stairs is approximately 15 to 16. However, the steps vary depending on the type of building, how fast one is and the height of the next floor above. Modern steps are usually 6 inches high.
15-17 depending on the height of the sub flooring of the next level. Not the ceiling height! The IRC ( international rail code ) says that step shall not exceed 7 3/4" . Typically there are 15 steps with rises between 7 1/2"- 7 3/4". There can only be a variance of 3/8" between ALL steps. Step depth must be at least 10" from nose to nose but makes absolutely no difference in step height. To calculate how many you need you will need to measure from finished ground level floor to finished second floor. Divide by 16. (16 risers for 15 steps) if it is less than 7 3/4" then that's your rise. If greater then try 17..... Ect and so on.