Stair Calculator
Plan a staircase: number of risers and treads, exact riser height, total run, stringer length and angle, with US code checks.
How it works
Enter the total rise from finished floor to finished floor, plus your preferred riser height and tread depth.
We round to a whole number of risers, then divide the rise evenly so every step is identical. There's always one fewer tread than risers, because the top floor acts as the last step.
Green and red badges check the US IRC limits (riser ≤ 7¾″, tread ≥ 10″) and the comfort rule 2R + T = 24-25″. A side-view drawing and stringer cut list help you lay out the boards.
Formula
N
Where:
- N
- = Number of risers
- rise
- = Total floor-to-floor height
- tread
- = Tread depth (excluding nosing)
Worked example
Total rise 108″, desired riser 7.5″, tread 10″.
108 ÷ 7.5 = 14.4 → 14 risers of 7.714″, 13 treads, total run 130″. Stringer = √(108² + 130²) = 169.01″, angle ≈ 39.7°.
Construction Tips for Solid Staircases
Achieving a professional staircase begins with an accurate measurement of the 'finished' floor-to-floor rise. Measure from the top of the flooring material on the lower level to the top of the finished floor on the upper level. Even a half-inch discrepancy creates a serious trip hazard that fails to meet IRC safety standards for step uniformity.
When cutting stringers, subtract the thickness of the tread material from the bottom riser and add it to the top riser. This adjustment ensures that once treads are installed, every step height remains identical. For stability, use at least three stringers for a 36-inch wide staircase to prevent bowing. Secure the top with metal hangers rather than relying solely on toe-nailing.
Code Compliance and Safety Pitfalls
Neglecting the headroom requirement is a common mistake. The IRC mandates a minimum vertical clearance of 80 inches measured from the sloped line formed by the tread nosings. In tight spaces like basements, failing to plan the ceiling opening early can lead to an unusable staircase. Ensure your layout leaves enough room for a landing as wide as the stairs.
Ensure your riser height stays within the '3/8 inch rule,' where the greatest riser height in a flight doesn't exceed the smallest by more than 3/8 of an inch. Double-check your work with a framing square and level at every step. Local building departments often have specific amendments to the IRC, so always confirm plans with a local inspector before buying lumber.
Frequently asked questions
The International Residential Code limits risers to 7¾ inches, with no more than ⅜″ variation between steps in a flight.
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For informational purposes only. This calculator does not provide professional engineering advice. Consult a qualified professional before making decisions based on these results.