What would the scale be of a doll house stairway that has 11 treads and each tread measures 2 1/8 inchs wide x 1 inch tall?

Provided it's intended to be scale-accurate, it's probably 1:8 scale.

Typical building codes specify a maximum riser height of 7-3/4 inches.  Which would be 31/32 inch at 1:8 scale.

The height of the stairway would equate to about 7-1/2 feet.  Which is actually pretty short.  

So in real life, either the riser height is too high, or the ceiling height is too low.

You need to tell us the dimensions in real life.  It's roughly 1/10th scale.