Stair Calculator
Calculate riser count, actual riser height, tread depth, total run, and stringer length. Includes building code compliance checks.
Total vertical height from finished floor to finished floor. Typical story height is 96-120 inches.
Ideal range: 7-7.75 inches
Minimum 10 inches per code
Code minimum is typically 36 inches for residential.
Building Code Compliance
How Stair Calculations Work
Building a staircase that is safe, comfortable, and code-compliant requires precise measurements and careful planning. The relationship between riser height, tread depth, and total rise determines every other dimension of your staircase. Even small errors in these measurements compound across multiple steps and can result in an uneven, dangerous, or non-compliant set of stairs. This calculator handles the math so you can focus on construction.
The 7-11 Rule and Building Codes
The most widely referenced guideline for residential stairs is the 7-11 rule, which recommends a riser height of approximately 7 inches and a tread depth of 11 inches. Most residential building codes in the United States set the maximum riser height at 7.75 inches and the minimum tread depth at 10 inches, based on the International Residential Code. The sum of one riser and one tread should ideally fall between 17 and 18 inches, a range that produces the most natural and comfortable stepping rhythm. Stairs that deviate significantly from this ratio feel either too steep or awkwardly shallow, increasing the risk of trips and falls.
Measuring Total Rise Accurately
The total rise is the single most critical measurement in stair building. It represents the exact vertical distance from the surface of the lower finished floor to the surface of the upper finished floor. Take this measurement at the precise location where the stairs will be installed, and measure at least three times to confirm accuracy. Account for any flooring materials that have not yet been installed. If the upper floor will have hardwood added later, include that thickness in your total rise. A measurement error of even half an inch spread across 14 risers creates noticeable unevenness that can cause stumbles.
Worked Example: Standard Basement Stairs
For a basement with a total rise of 108 inches (9 feet floor to floor), dividing by a target riser height of 7.5 inches gives 14.4, which rounds up to 15 risers. The actual riser height becomes 108 divided by 15, equaling 7.2 inches per step. With 15 risers you get 14 treads, and at 10 inches each, the total run is 140 inches (11 feet 8 inches). The stringer length is the square root of 108 squared plus 140 squared, which equals roughly 176.8 inches (14 feet 9 inches). The riser-plus-tread sum of 17.2 inches falls right in the ideal range.
Common Stair-Building Mistakes
The most frequent error is failing to account for finished floor thickness in the total rise measurement. Another common mistake is inconsistent riser heights, which is both a code violation and a serious tripping hazard. Every riser in a flight must be within 3/8 inch of every other riser. Builders sometimes forget that the number of treads is always one fewer than the number of risers because the upper floor serves as the final step. Cutting stringers too thin at the notch points weakens the structure, so always maintain at least 3.5 inches of solid wood below each tread notch. Finally, forgetting to factor in nosing overhang can throw off total run calculations.
When You Need a Landing
Building codes typically require a landing when a staircase rises more than 12 feet vertically. Landings must be at least as deep as the stair width, usually 36 inches minimum. L-shaped and U-shaped staircases use landings to change direction, and these configurations are useful when horizontal space is limited. A landing also provides a resting point, which is especially important for taller staircases. When planning a landing, remember that it effectively splits your staircase into two separate flights, and each flight needs its own rise and run calculations.