Stair Stringer Calculator
Use this free stair stringer calculator to estimate the number of risers and treads, actual riser height, total stair run, stair angle and approximate stringer length. Enter the total rise, target riser height and tread depth to plan a consistent stair layout.
Stair dimensions
How to calculate stair stringers
Start by measuring the total vertical rise from the finished lower floor to the finished upper floor. This measurement is the full height the stairs must climb.
Divide the total rise by your desired riser height to estimate the number of risers. Use a practical whole-number riser count, then divide the total rise by that count to get the actual equal riser height.
In a common stair layout, the number of treads is one less than the number of risers because the upper floor acts as the final stepping surface.
Multiply the tread count by the tread depth to calculate the total horizontal run of the stairs.
The calculator then uses the total rise and total run to estimate the diagonal stair stringer length and stair angle.
If you also need to estimate framing lumber for the project, use the Lumber Calculator. To calculate the volume of dimensional lumber, use the Board Foot Calculator.
Stair layout example
Total rise: 108 in
Target riser: 7.5 in
Tread depth: 10 in
Stringer planning
Stair stringer length calculator
The stair stringer is the diagonal framing member that supports the stair treads and risers. Its approximate diagonal length can be estimated from the total stair rise and total run.
Once the riser count and tread count are known, the calculator finds the total horizontal run and uses it with the total rise to estimate the stringer length.
The calculated length is useful for planning material, but actual cutting and installation can require extra material for end cuts, bearing and site conditions.
Stringer length formula
Approximate stringer length =
This is the diagonal distance calculated using the Pythagorean theorem.
Stair angle calculator
Stair angle describes the slope of the staircase. This calculator estimates the angle from the total rise and total horizontal run.
Rise vs. run
Rise is the vertical height of each step, while run refers to the horizontal depth or distance covered by the stair treads. Both measurements affect the overall slope and footprint of the staircase.
Always verify the final stair layout against the building requirements that apply to your location and project before construction.
Stair stringer calculator FAQs
How many stair risers do I need?
Divide the total rise by your target riser height to estimate the riser count. The calculator uses a whole-number count and then recalculates the actual equal riser height.
How do I calculate the actual riser height?
Divide the total vertical rise by the final number of risers. This gives an equal riser height for every step.
Why are there fewer treads than risers?
In many stair layouts, the upper floor acts as the final stepping surface, so the tread count is typically one less than the riser count.
How is total stair run calculated?
Multiply the number of treads by the tread depth. For example, 13 treads at 10 inches each create a total run of 130 inches.
What does stringer length mean?
Stringer length is the approximate diagonal distance from the bottom of the stair run to the top of the total rise.
How is stair angle calculated?
The stair angle is calculated from the total rise and total run using the arctangent of rise divided by run.
Can I use this calculator to cut stair stringers?
Use the calculator for planning dimensions and estimates, but verify measurements, material allowances and applicable building requirements before making final cuts.
Does this calculator replace building-code requirements?
No. Building requirements vary by location and project type, so check the rules that apply to your project before construction.