Use this Stair Rise & Run Calculator to evaluate an equal-step layout from total rise, a chosen number of risers, and either tread run or total horizontal run. Review exact riser height, tread dimensions, stair angle and the proportional stair diagram.
Enter the layout you want to test
This tool does not choose the riser count for you. Enter a whole number of risers, then solve from tread run or total run.
Your equal-step geometry
Review the exact riser, tread run, total run, angle and sloped flight length.
Transparent calculation
How rise and run are calculated
The selected riser count divides the total rise into equal vertical steps. The horizontal side comes from either your tread run or total-run input.
total rise ÷ risersrisers − 1treads × tread runtotal run ÷ treadsatan(total rise ÷ total run)√(rise² + run²)Important: this tool evaluates dimensions and geometry. It is not structural approval or a substitute for locally adopted requirements.
Step by step
How to use the Stair Rise & Run Calculator
Use this tool when you already want to evaluate a particular whole-number riser count. Enter the total vertical rise, choose how many equal risers the flight should contain, then provide either the run of one tread or the total horizontal run available to the simple flight model.
- Measure total rise between the finished lower and upper walking surfaces.
- Enter a whole-number riser count you want to test.
- Choose Tread run if you know the horizontal depth of each step, or Total run if you know the overall footprint.
- Calculate to see exact equal riser height, tread run, total run, angle and sloped length.
- Review the dimensions against the requirements and construction details that apply to your project.
If you want BuildCalcForge to choose a riser count from a maximum-riser setting, start with the Stair Calculator.
Read your result
What the rise and run results mean
Exact riser height
Total rise divided equally across the whole-number riser count you entered.
Number of treads
For this simple floor-to-floor model, the number of horizontal treads is one less than the number of risers.
Tread run
The horizontal distance assigned to each tread in the geometric calculation.
Total run
The horizontal footprint created by all calculated tread runs.
Stair angle
The angle of the overall flight envelope relative to horizontal, calculated from total rise and total run.
Sloped flight length
The straight diagonal distance from the bottom to the top of the calculated rise/run triangle.
Worked example
Example: 9 ft rise with 14 risers and 10 in tread run
Suppose the total rise is 108 in, you want to test 14 risers, and each tread run is 10 in.
108 ÷ 14 ≈ 7.714 in14 − 1 = 1313 × 10 = 130 inatan(108 ÷ 130) ≈ 39.7°The geometric flight is about 169 in along the slope. Those numbers describe the simplified equal-step layout; construction details still need separate verification.
Measure consistently
Rise and run measurement tips
- Measure finished surface to finished surface whenever finish thicknesses are known.
- Do not mix rough-framing dimensions with finished-floor dimensions without accounting for the difference.
- Use one horizontal reference convention consistently throughout the flight.
- If total run is fixed, remember that changing the riser count changes the calculated tread run.
- Recheck site dimensions before cutting stringers or ordering project-specific material.
Know the limits
Assumptions and limitations
This calculator models a straight stair flight with equal risers and equal tread runs. It assumes the upper floor acts as the final walking surface, giving one fewer tread than risers. It does not calculate landings, winders, curved stairs, nosings, headroom, guards, handrails, structural stringer design, connectors or site-specific framing details.
Use the result as planning geometry, then verify the requirements adopted where the project is located and the details needed for the actual stair system.
Planning reference
Model-code context for common stair dimensions
The default examples used across BuildCalcForge often reference the 2021 International Residential Code model-code values of a riser not more than 7¾ in and tread depth not less than 10 in for the stair conditions covered by Sections R311.7.5.1 and R311.7.5.2. This calculator does not automatically approve a layout against every applicable requirement.
Local jurisdictions may adopt different editions or amendments, and special stair types can have different provisions. Treat the calculator as a transparent planning aid rather than a permit or inspection decision.
International Code Council — 2021 IRC, Chapter 3 ↗Common questions
Stair Rise & Run Calculator FAQ
What is the difference between stair rise and stair run?
Rise is vertical movement. Run is horizontal movement. A single riser and tread create the repeated step geometry, while total rise and total run describe the whole simplified flight.
Why does this calculator ask for the number of risers?
This page is designed to evaluate a specific riser count. If you want a calculator to choose the riser count automatically from a maximum-riser setting, use the main Stair Calculator.
Can I calculate tread depth from total run?
Yes. Select Total run, enter the overall horizontal run and riser count, and the calculator divides the total run equally across the calculated number of treads.
Can I enter fractional inches?
Yes. US fields accept entries such as 7 3/4, 10 1/2 and decimal equivalents.
Does the stair angle determine whether the stair is code compliant?
No. Angle is a useful geometric description, but compliance depends on the adopted requirements and the full stair design, not one angle value.
Can I use metric measurements?
Yes. Switch to Metric to enter millimeters and receive metric result dimensions.
Sources & methodology
How this calculator is checked
The tool uses standard equal-step and right-triangle geometry, retains full mathematical precision internally, and separates geometry from construction approval.