The "27 Rule" for stairs is a helpful guideline for determining comfortable stair dimensions. According to this rule, the sum of the riser height and the tread depth should equal 27 inches. For example, if the riser height is 7 inches, the tread depth should be 10 inches.

Straight Staircase Because of the basic design, this is the cheapest staircase style, with installation costs between $2,000 and $5,000.

There is no set of absolute rules for modern English that predicts when a series of structures consisting of a riser and a tread is called stairs and when it's called steps, but we can make some generalizations based on use: When they're outside, they're more often called steps than they are called stairs.