A staircase calculator determines the exact riser height, tread depth, and number of steps from your floor-to-floor height — and checks everything against IRC building code. Getting these numbers right before cutting stringers saves expensive rework and ensures a comfortable, safe staircase.
Staircase Dimensions
Measure from finished floor to finished floor (include both floor finishes). Enter in inches.
IRC Code Compliance Check
Staircase Dimensions
How to Use the Staircase Calculator
Building a staircase that's comfortable to walk and passes inspection requires precise calculations before you cut a single piece of lumber. The staircase calculator takes your floor-to-floor height and desired tread depth, then produces the exact riser count, riser height, stringer length, and IRC code compliance status for each dimension.
Step 1: Measure Total Rise
The total rise is the distance from the finished floor at the bottom to the finished floor at the top — including the thickness of any flooring (hardwood, tile, carpet padding) on both floors. Measure at the actual stair location, not just from structural subfloor to subfloor. Enter the measurement in inches for the most precise result.
Step 2: Set Tread Depth
The IRC minimum tread depth is 10 inches, measured from nosing to nosing. Most comfortable residential stairs use 10.5–11 inches. Deeper treads feel more natural but require more horizontal space. The total horizontal footprint of the staircase equals (number of treads) × (tread depth), so a deeper tread makes a longer staircase.
Step 3: Check IRC Compliance
The calculator checks three IRC R311.7 requirements: maximum riser height of 7-3/4 inches; minimum tread depth of 10 inches; and maximum variation between any two adjacent risers of 3/8 inch. A red "Fail" on any check means the staircase as designed would not pass residential inspection — adjust the tread depth or accept fractional riser heights.
Step 4: Review Stringer Length
The stringer is the angled board that supports both the treads and risers. Its length is computed as the hypotenuse of the rise/run triangle: √(totalRise² + totalRun²). For a typical 9-foot ceiling (108-inch rise) with 10.5-inch treads, the stringer is roughly 198 inches (16.5 feet). Most lumber yards carry 2×12 boards up to 20 feet for stringers.
Step 5: Apply to Lumber Order
A standard residential staircase needs 3 stringers (2 outer + 1 center for stairs wider than 36 inches). Each stringer is cut from a 2×12, so round the stringer length up to the next standard board length (8, 10, 12, 14, 16, or 20 feet). Treads are typically 2×10 or 2×12 boards at stair width length. Risers are typically 1×8 boards.
FAQ
Is this staircase calculator free to use?
Yes, the staircase calculator is completely free with no signup required. All calculations run locally in your browser — your measurements are never sent to any server. No account or payment needed.
Is my data private when I use this tool?
Absolutely. Every calculation runs in your browser locally. No measurements, dimensions, or project details are ever transmitted to a server. Your data stays entirely on your device.
What is the IRC building code for stair risers?
Per the International Residential Code (IRC R311.7): maximum riser height is 7-3/4 inches (196mm); minimum tread depth is 10 inches (254mm); maximum variation between any two risers in the same stair run is 3/8 inch (9.5mm). This calculator checks all three requirements and shows pass/fail status.
How do I calculate stair rise and run?
Start with the total floor-to-floor height (total rise). Divide by 7 (ideal riser height) to get the approximate number of risers. Round to the nearest whole number, then divide the total rise by that number to get the exact riser height. The tread depth is typically 10-11 inches for residential stairs.
What is a stair stringer?
A stringer is the diagonal board that supports the treads and risers on each side of the staircase. Its length equals the square root of (total rise² + total run²). A standard residential staircase needs two or three stringers depending on stair width. The calculator computes the stringer length for lumber ordering.
What is the ideal stair angle?
Comfortable residential stairs typically have an angle between 30-35 degrees. Steeper stairs (above 40 degrees) are harder to climb; shallower stairs (below 25 degrees) feel uncomfortably long. The calculated angle is shown so you can confirm the staircase will feel natural in the space.
How does the calculator handle fractional riser heights?
The calculator divides the total rise by the computed number of risers to get an exact riser height that's often a fraction. It shows this to 3 decimal places so you can accurately cut your stringers. The IRC variation check ensures no two risers differ by more than 3/8 inch — an important safety requirement.
Can I switch between inches and metric?
Yes. Toggle between imperial (feet/inches) and metric (meters/centimeters) using the unit switch. All inputs and results update automatically. The IRC code thresholds are also displayed in both measurement systems.