I know how to calculate the rise and tread of a staircase, b...

[Softy]

I know how to calculate the rise and tread of a staircase, but what is the calculation for the length of stringer you need?

[syfd2004]

How many steps are you installing? syfd2004

[Softy]

It is 102" from the floor to the landing, but I need to know the formula for future projects also.

[syfd2004]

Here is how you figure the length of you stringer.
Take your Total Rise in inches and multiple it by itself
Then take Total Run in inches and multiple it by itself
Then add them together
The stringer length is the square root of that total, add 12 to 18" for waste.

For expample lets use your 102" total rise and lets say your total Run is 150", 102 x 102=10404 / 150 x 150=22500
10404 + 22500 = 32904
the square root of 32904 is 181.39" or approx. 17' with waste.

Let me know if this helps
syfd2004