Part of the Construction collection — 4 tools available
Stair Calculator — Rise, Run & Stringer
Calculate stair dimensions including number of risers, tread depth, total run, and stringer length. Design code-compliant stairs for decks and interiors.
About This Calculator
Building stairs requires precise calculations to meet building codes and feel comfortable underfoot — getting the math wrong means stairs that are too steep, too shallow, or simply don't fit the space. The International Residential Code limits riser height to 7¾ inches maximum and requires a minimum 10-inch tread depth for safe use. Every fraction of an inch matters because small errors compound across every step. Our stair calculator determines the ideal number of risers, actual riser height, total run, and stringer length for code-compliant stairs that feel natural to walk on.
The Formula Behind This Calculator
Rise per step = Total rise / Number of steps Run per step ~ 10 inches Total run = Steps * Run per step
Understanding the math helps you verify results and make better decisions for your project.
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How to Use
- 1Measure the total rise from finished floor to finished floor.
- 2Enter your desired riser height (7 inches is a comfortable target).
- 3Set the tread depth — 11 inches is standard for residential stairs.
- 4Review the number of risers, actual rise, total run, and stringer length.
When to Use
- →Building deck stairs and determining stringer layout.
- →Planning interior staircases between floors.
- →Verifying existing stair dimensions meet building code requirements.
Tips
- ✓The 2R + T rule (twice the rise plus the tread) should equal 24-25 inches for comfortable stairs.
- ✓All risers in a flight must be within 3/8 inch of each other per IRC code.
- ✓Use 2×12 lumber for stair stringers and cut at least 3 stringers for 36-inch wide stairs.
FAQ
What is the maximum riser height allowed by code?
The International Residential Code (IRC) allows a maximum riser height of 7¾ inches (197 mm) for residential stairs. Commercial buildings follow IBC which limits risers to 7 inches.
How many stringers do I need for my stairs?
Stringers should be spaced no more than 36 inches apart for 2× treads, or 30 inches for 5/4 decking. For a 36-inch wide staircase, use 3 stringers; for 48 inches, use 4.
What's the ideal rise-to-run ratio?
A 7-inch rise with an 11-inch run is the most common and comfortable ratio for residential stairs. The Rule of 25 (2×rise + run ≈ 25 inches) is a good target for comfortable stairs.
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