Stair Stringer Calculator
Calculate stair risers, tread count, actual riser height, total run, stair angle and approximate stringer length.
How to calculate stair stringers
Start by measuring the total vertical rise from the finished lower floor to the finished upper floor.
Divide the total rise by your desired riser height to estimate the number of risers. Then divide the total rise by that whole-number riser count to get the actual, equal riser height.
In a typical stair layout, the number of treads is one less than the number of risers. Multiply the tread count by the tread depth to estimate the total run.
The approximate stringer length is calculated from the total rise and total run using the Pythagorean theorem.
Example layout
Total rise: 108 in
Target riser: 7.5 in
Tread depth: 10 in
Frequently asked questions
How many stair risers do I need?
Divide the total rise by your desired riser height and round to a practical whole number, then recalculate the exact riser height.
Why are there fewer treads than risers?
In many stair layouts, the upper floor acts as the final stepping surface, so tread count is typically one less than riser count.
What does stringer length mean?
It is the approximate diagonal length from the bottom of the stair run to the top of the total rise.
Does this replace local building-code requirements?
No. Always verify your final stair dimensions against applicable local building codes before construction.