Stair Calculator
Enter the total rise (floor-to-floor height) and your desired step dimensions to calculate the number of risers, exact rise and run per step, total stair run, and stringer length.
Floor-to-floor height (including finished floor thickness)
Code max: 7¾" (7.75")
Code min: 10" (tread nose to nose)
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Number of risers
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Actual rise per step
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Run per step
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Total run (horizontal)
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Stringer length
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Stair angle
Stair Terminology
- Rise — the vertical height of one step
- Run (tread depth) — the horizontal depth of one step, measured from nosing to nosing
- Stringer — the diagonal board (or steel) that supports the treads and risers; the hypotenuse of the stair triangle
- Total rise — the floor-to-floor height; the sum of all individual rises
- Total run — the horizontal distance the staircase occupies; the sum of all treads
Building Code Requirements (IRC)
Most residential building codes in the United States follow the International Residential Code (IRC):
| Dimension | IRC requirement |
|---|---|
| Maximum riser height | 7¾ inches (7.75") |
| Minimum tread depth | 10 inches (nosing to nosing) |
| Minimum stair width | 36 inches clear |
| Maximum variation between risers | ⅜ inch |
| Handrail required when | 4 or more risers |
| Maximum baluster spacing | 4 inches (sphere test) |
| Minimum headroom | 6 ft 8 in (80") |
Local codes may be stricter. Always verify with your local building department before starting construction.
Comfortable Stair Design
The most comfortable stairs satisfy the rule of 17 to 18: rise + run should equal 17–18 inches. A 7" rise + 11" run = 18 — a comfortable, commonly-used combination.
| Rise | Run | Total | Comfort |
|---|---|---|---|
| 6" | 12" | 18 | Very comfortable (low slope) |
| 7" | 11" | 18 | Standard comfortable |
| 7.5" | 10" | 17.5 | Acceptable; steeper feel |
| 7.75" | 10" | 17.75 | Code limit; steep |
Stringer Sizing
A stringer cut from standard lumber must retain adequate uncut depth at any point. The IRC requires a minimum 3.5-inch net section (uncut depth) on a notched stringer. Most stringers are cut from 2×12 lumber. For stairs wider than 36 inches, a centre stringer is typically required.
Frequently Asked Questions
How do I calculate the number of stairs?
Divide the total rise (in inches) by your desired rise per step, then round to the nearest whole number. The actual rise per step equals the total rise divided by that rounded number. This calculator does all of that automatically.
Why is my actual rise different from my desired rise?
The total rise must be divided evenly among a whole number of risers. If your total rise is 109 inches and you want 7-inch risers, you get 15.57 risers — you must round to either 15 or 16. Each option gives a slightly different actual rise per step.
How long should my stair stringers be?
Stringer length is the hypotenuse of the right triangle formed by the total rise and total run: √(rise² + run²). Add a few inches for the bottom cut that rests on the floor and the top cut that sits against the header joist.
