Stair Calculator
A 9-foot floor-to-floor height (108 inches) with 7.5-inch risers needs 15 steps and a total run of about 11 feet 8 inches. This stair calculator figures out step count, adjusted riser height, total run, stair angle, and stringer length from your measurements. Enter the total rise from one finished floor to the next, pick a target riser height and tread depth, and the calculator does the rest.
Quick answer
Total rise divided by target riser height gives the number of steps (rounded up).
What this tells you
- •Total rise divided by target riser height gives the number of steps (rounded up).
- •Total run equals the number of treads (steps minus one) multiplied by tread depth.
- •Stringer length is the diagonal distance from top to bottom of the staircase.
How to Use
- 1Measure the total rise from one finished floor level to the next in inches.
- 2Enter a target riser height (7.5 inches is a comfortable default).
- 3Enter a target tread depth (10 inches meets the IRC minimum).
- 4Click Calculate to see the number of steps, adjusted riser height, total run, angle, and stringer length.
- 5Adjust riser height or tread depth and recalculate until the dimensions fit your space.
How It Works
Formula
Number of Steps = ceil(Total Rise / Riser Height)
Adjusted Riser = Total Rise / Number of Steps
Total Run = (Steps - 1) x Tread Depth
Angle = atan(Adjusted Riser / Tread Depth)
Stringer = sqrt(Total Rise^2 + Total Run^2)The step count is rounded up so the adjusted riser height stays equal to or shorter than the target. Total run uses one fewer tread than the step count because the top step lands on the upper floor. Stringer length is the hypotenuse of the rise-run right triangle.
Calculation note: values are processed in the order shown above, using the current input units.
Worked Examples
Standard 9-foot ceiling (108 in total rise)
Short deck staircase (24 in total rise)
Steps by Total Rise and Riser Height
Number of steps for common floor-to-floor heights at three popular riser heights. Step count is rounded up so adjusted risers stay within the target range.
| Total Rise | 7.00 in riser | 7.25 in riser | 7.50 in riser |
|---|---|---|---|
| 84 in (7 ft) | 12 steps | 12 steps | 12 steps |
| 96 in (8 ft) | 14 steps | 14 steps | 13 steps |
| 108 in (9 ft) | 16 steps | 15 steps | 15 steps |
| 120 in (10 ft) | 18 steps | 17 steps | 16 steps |
These counts assume a single straight run. L-shaped or U-shaped staircases with landings split the rise across two runs but keep the same total step count.
What Is the IRC Stair Code?
The International Residential Code (IRC) sets minimum standards for residential staircase dimensions in the United States. Most local jurisdictions adopt the IRC with minor amendments, so these numbers apply in the majority of new-construction and remodel projects.
Maximum riser height is 7.75 inches. Every riser in a flight must be within 3/8 inch of every other riser. Minimum tread depth is 10 inches, measured from nosing to nosing. Minimum clear width is 36 inches, measured between finished walls or between a wall and the edge of the guardrail.
These rules exist to reduce fall risk. A riser taller than 7.75 inches forces an uncomfortably steep climb, and a tread shallower than 10 inches does not give enough foot contact for safe descent. Always check with your local building department before finalizing stair dimensions.
Common mistakes
- Forgetting to account for finished floor thickness at the top and bottom, which changes total rise by 0.75 to 1.5 inches
- Not including a landing when the staircase turns, which adds to the total horizontal footprint
- Using a riser height outside the code range and failing inspection
- Measuring total rise from subfloor to subfloor instead of finished floor to finished floor