Stair Calculator
Designing stairs the right way is critical for safety, comfort, and code compliance. Our free online Stair Calculator helps you calculate stair rise, run, stringer length, step height, tread depth, and stair angle in seconds. Whether you're a seasoned contractor or a DIY enthusiast, this tool saves time and removes guesswork from stair construction.
This page includes both an Automatic Stair Calculator and a Manual Stair Calculator so you can choose the workflow that suits your project. Enter your dimensions, click calculate, and get instant, code-ready results.
Automatic Stair Calculator
Manual Stair Calculator
Calculation Results
How to Use the Stair Calculator
Automatic Calculator
- Enter Total Rise (A): The vertical distance from finished floor to landing.
- Input Target Step Height (F): Your preferred riser height.
- Set Tread Thickness (C) & Tread Depth (B): Define the walking surface.
- Select Mount Type: Standard or Flush stringer.
- Click "Calculate": Instantly see the number of steps, stringer length, stair angle, and placement.
Manual Calculator
If you already know your Total Rise and Total Run, or want full control of riser count, the manual tool is perfect:
- Enter Total Rise (A) and Total Run (G).
- Define Number of Steps, Tread Thickness, and Mount Type.
- Hit "Calculate" for detailed dimensions, including Step Height, Tread Depth, Stringer Length, and Stair/Rail Angle.
Why Use an Online Stair Calculator?
Building a staircase requires precise math. Miscalculations lead to uncomfortable steps, tripping hazards, and failed inspections. Our calculator applies industry-standard formulae like the renowned Blondel formula (2 × Riser + 1 × Tread ≈ 25 in / 63–65 cm) to create stairs that are safe, comfortable, and aesthetically balanced.
Accurate Results
Automatic computation of rise, run, and stringer length.
Compliant Design
Aligns with common IRC/IBC stair building codes.
Time Saving
Instant calculations eliminate tedious manual math.
User Friendly
Simple inputs with clear outputs for builders of all levels.
Mobile Friendly
Use it on-site, on any device.
Essential Stair Terminology (Glossary)
To build confidently, familiarize yourself with key terms:
Riser (Rise)
The vertical part between treads.
Tread (Run)
The horizontal surface you step on.
Stringer
The inclined support board carrying treads and risers.
Headroom
Clear vertical space above the stair nosing (minimum 6′8″ per code).
Nosing
The protruding edge of a tread, improving safety and comfort.
Stair/Rail Angle
The slope of the stairs, used for rail and baluster cuts.
Understanding Code & Best Practices
Our calculations follow widely accepted guidelines:
Always double-check your layout on site and allow for tread and riser adjustments at the top step.
Frequently Asked Questions
What is stair calculation?
It's the process of defining precise dimensions—rise, run, tread, riser, and stringer—so your stairs are safe, functional, and code-compliant.
Can I calculate stair stringers online?
Yes. Enter your rise, run, and dimensions into the calculator and instantly get stringer layout details.
Is this calculator beginner-friendly?
Absolutely. The Automatic Mode guides you step by step, while the Manual Mode lets pros fine-tune every variable.
Are the results accurate?
The tool uses proven algorithms and the Blondel formula for optimal stride and code compliance.
Boost Your Projects With Precision
Whether you're building a deck staircase, an interior stairway, or remodeling an old flight of stairs, our Stair Stringer Calculator eliminates costly mistakes and streamlines your workflow. Get started today – accurate rise, run, and stringer dimensions are only a few clicks away.
Start Calculating Now