The length of a staircase, including the number of steps, can vary depending on factors like the height of each step, tread length, building code, construction requirements and the angle of the staircase.

A typical stairway consists of riser, run, landing and flight. Riser refers to the vertical part of a step or stair. It’s the height between one step and the next. The average riser height should be 7 to 7-1/2 inches, maximum is about 7-3/4 inches, minimum is about 4 inches, but however, many homeowners kept it about 7 inches.

Run is the horizontal part of a step or stair. It’s the depth or length of the stair tread, the part you step on. The average run length should be 10 inches without nosing and 11 inches with nosing.

In general, a typical 15 step staircase should be 195 inches (or 16.25 feet, or 4.95 meters) long, while a typical 14 step staircase should be 182 inches (or 15.17 feet, or 4.62 meters) long.

Likewise, a typical 12 step staircase should be 156 inches (or 13 feet, or 3.96 meters) long, while a typical 13 step staircase should be 169 inches (or 14 feet, or 4.27 meters) long.

Stairs typically consist of a series of steps that allow people to ascend or descend between different levels in a building or structure. Each step consists of a horizontal tread and a vertical riser. The incline length of one step is about 13 inches if riser height is 7 inches and tread length is 10 inches.

Assuming a standard step depth of around 13 inches (33 centimeters), the total length of a 15-step staircase would typically be around 195 inches or 16.25 feet (4.95 meters).

To calculate the length of staircase for a 12 steps, you just need to multiply 12 steps by 13 inches incline length per step, such as length of staircase for 12 steps = total steps x 13, so 12 x 13 = 156 inches or 13 feet (3.96 meters).

To calculate the length of staircase for 15 stairs with a run of 11 inches and a rise of 7 inches, and a total of 15 steps, we can use the Pythagorean theorem to find the length of the handrail along the incline.

- Calculate the length of each step’s diagonal:using the Pythagorean theorem: diagonal = √(rise)2 + (run)2 = √7^2 + 11^2 = √121 + 49 = √170 = 13 inches.
- Multiply the length of diagonal by the number of steps (stairs): Total staircase length = diagonal × number of steps, such as 13″×15 = 195 inches or 16.25 feet (4.95 meters) long.

Here’s are general guideline for how long is a 12, 13, 14 and 15 step staircase:

- The length of a 12-step staircase must be 156 inches or 13 feet (3.96 meters) long. The staircase length for 12 steps = 13″×12 = 156″.
- The length of a 13-step staircase must be 169 inches or 14 feet (4.27 meters) long. The staircase length for 13 steps = 13″×13 = 169″.
- The length of a 14-step staircase must be 182 inches or 15.17 feet (4.62 meters) long. The staircase length for 14 steps = 13″×14 = 182″.
- The length of a 15-step staircase must be 195 inches or 16.25 feet (4.95 meters) long. The staircase length for 15 steps = 13″×15 = 195″.

Conclusions:

The length of a 12-step staircase need to be 156 inches or 13 feet (3.96 meters), a 13-step staircase must be 169 inches or 14 feet (4.27 meters) long, a 14-step staircase have to be 182 inches or 15.17 feet (4.62 meters) long, and a 15-step staircase should be 195 inches or 16.25 feet (4.95 meters) long.