Measure from finished floor to finished floor. Standard story height is 96 to 120 inches.
Leave blank for automatic calculation.
Leave blank to calculate from riser using comfort rule.
Your Results
Enter total rise and click calculate.
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What This Calculator Does
This stair calculator determines the number of risers and treads, individual riser height, tread depth, total run, stringer length, and stair angle for any given floor-to-floor height. It checks compliance with both the International Building Code (IBC) for commercial buildings and the International Residential Code (IRC) for homes. The tool uses the Blondel comfort formula (2R + T = 24 to 25) to optimize the riser-tread relationship when dimensions are not specified.
The Formula
The total rise (floor-to-floor height in inches) is divided by the target riser height to determine the number of risers. The number of treads is always one less than the number of risers because the top floor serves as the final tread. The total run is the horizontal distance the stair covers. Stringer length is calculated using the Pythagorean theorem. The 2026 IRC limits risers to a maximum of 7.75 inches and requires a minimum tread depth of 10 inches. The IBC limits risers to 7 inches with 11-inch minimum treads.
Step-by-Step Example
Measure total rise
Measure from finished floor to finished floor. Example: 108 inches (9 ft floor-to-floor height).
Select building code
Choose IRC for residential or IBC for commercial. The calculator adjusts riser and tread limits accordingly.
Review the layout
108" / 7.25" target = 15 risers at 7.2" each. Using Blondel formula: 10.6" treads. 14 treads x 10.6" = 148.4" total run (12.4 ft).
Verify compliance
Riser 7.2" is under the IRC max of 7.75" and the IBC max of 7". Tread 10.6" meets the IRC minimum of 10" but falls short of the IBC 11" minimum.
Real-World Use Cases
New Home Construction
Design stair framing dimensions for new residential construction that comply with the IRC and local amendments.
Deck and Porch Stairs
Calculate exterior stair dimensions from deck or porch elevation down to grade level.
Commercial Renovation
Verify that replacement stairs in commercial buildings meet IBC requirements for riser uniformity and tread depth.
Common Mistakes to Avoid
Measuring floor-to-floor height before finished flooring is installed. The finish materials (tile, hardwood, carpet) change the total rise, which changes every riser height.
Making the top or bottom riser a different height than the others. Building codes require that riser heights not vary more than 3/8 inch across the entire stairway.
Forgetting nosing overhang. IRC allows up to 1.25 inches of nosing beyond the tread below, and IBC allows 0.75 to 1.25 inches. Nosing does not count toward tread depth.
Not accounting for headroom clearance. Both IBC and IRC require a minimum of 6 ft 8 inches (80 inches) of headroom measured vertically from the tread nosing to any overhead obstruction.
Frequently Asked Questions
Accuracy and Disclaimer
Stair dimensions must comply with your local building code, which may differ from the model IBC or IRC. This calculator references the 2024/2026 model codes. Local jurisdictions may adopt amendments that change maximum riser heights, minimum tread depths, or other requirements. Always verify with your local building department before construction.
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