Stair Calculator
Calculate stair dimensions including number of risers, tread depth, and total run from floor-to-floor height.
This free online stair calculator provides instant results with no signup required. All calculations run directly in your browser — your data is never sent to a server. Enter your values below and see results update in real time as you type. Perfect for everyday calculations, homework, or professional use.
Floor-to-floor height in inches (9 ft = 108 in)
Minimum: 0
Ideal riser height (7 to 7.75 in typical)
Depth of each tread (10 to 11 in typical)
Results
Number of Risers
14
Actual Riser Height
7.714 in
Number of Treads
13
Total Run
10.83 ft
Stringer Length
169 in
How to Use This Calculator
Enter your input values
Fill in all required input fields for the Stair Calculator. Most fields include unit selectors so you can work in your preferred unit system — metric or imperial, whichever matches your problem.
Review your inputs
Double-check that all values are correct and that you have selected the right units for each field. Incorrect units are the most common source of calculation errors and can produce results that are off by factors of 2, 10, or more.
Read the results
The Stair Calculator instantly computes the output and displays results with units clearly labeled. All calculations happen in your browser — no loading time and no data sent to a server.
Explore parameter sensitivity
Try adjusting individual input values to see how the output changes. This is a quick and effective way to develop intuition about how different parameters influence the result and to identify which inputs have the largest effect.
Formula Reference
Stair Calculator Formula
See calculator inputs for the governing equation
Variables: All variables and their units are labeled in the calculator interface above. Input fields accept values in multiple unit systems — select your preferred unit from the dropdown next to each field.
When to Use This Calculator
- •Use the Stair Calculator when you need accurate results quickly without the risk of manual computation errors or unit conversion mistakes.
- •Use it to verify calculations made by hand or in spreadsheets — an independent check can catch errors before they lead to costly decisions.
- •Use it to explore how changing input parameters affects the output — a quick way to develop intuition and identify the most influential variables.
- •Use it when collaborating with others to ensure everyone is working from the same numbers and applying the same assumptions.
About This Calculator
The Stair Calculator is a free, browser-based calculation tool for engineers, students, and technical professionals. Calculate stair dimensions including number of risers, tread depth, and total run from floor-to-floor height. It implements standard formulas and supports both metric (SI) and imperial unit systems with automatic unit conversion. All calculations are performed instantly in your browser with no data sent to a server. Use this calculator as a quick reference and sanity-check tool during design, analysis, and learning. Always verify results against primary engineering references and applicable standards for any safety-critical application.
About Stair Calculator
Designing stairs that are comfortable and code-compliant requires balancing riser height, tread depth, and available floor space. This calculator determines the number of risers, actual riser height, number of treads, total horizontal run, and stringer length based on the floor-to-floor height and your desired dimensions. Building codes typically require risers between 7 and 7-3/4 inches and treads at least 10 inches deep. The stair rule of thumb states that two risers plus one tread should equal 24 to 25 inches for comfortable climbing. Getting these proportions right prevents the stairs from feeling too steep or too shallow, and ensures safety for everyday use.
The Math Behind It
Formula Reference
Risers
Risers = round(Total Rise / Desired Riser Height)
Variables: Total rise in inches
Total Run
Run = (Risers - 1) x Tread Depth
Variables: Number of treads is always one less than risers
Worked Examples
Example 1: 9-foot ceiling (108 inches total rise)
Total Rise = 108 in, Desired Riser = 7.5 in, Tread = 10 in
You need 14 risers at 7.71 inches each, with a total run of 10.83 feet.
Common Mistakes & Tips
- !Forgetting that the number of treads is one less than the number of risers.
- !Not verifying that the actual riser height meets building code maximums.
- !Ignoring the comfort rule (2R + T = 24-25 inches).
- !Not accounting for floor finish thickness in the total rise measurement.
Related Concepts
Used in These Calculators
Calculators that build on or apply the concepts from this page:
Frequently Asked Questions
What is the ideal riser height?
Most people find stairs most comfortable with risers between 7 and 7-1/2 inches. Building codes allow a maximum of 7-3/4 inches.
Why is there one fewer tread than riser?
The upper floor acts as the final tread. So if you have 14 risers, you have 13 separate treads, plus the landing at the top.