As with the majority of my models, this is designed with components and groups for ease of modifying either the textures or in this case to make this staircase fit in your model.
It makes a full circle from top to bottom. Each tread is 8 inches above the last, for a total height fro ground to second story of 10 feet.
THere ar eline squares (groups within the model) for ease of placement. Simply place and then open the compoent to remove.
Its full diameter is 6 feet.