Stair Rise and Run Calculator
Stair rise and run calculator for safe, code-compliant stairs. Enter total floor-to-floor height to get the number of risers, riser height, tread depth, and total run, with an IRC building code check (riser max 7.75 inches, tread min 10 inches).
To calculate stair rise and run, divide the total floor-to-floor height by your target riser height (7 to 7.75 inches is typical) and round to a whole number of risers. Tread count is risers minus 1. For 108 inches of total rise, plan 14 risers at 7.71 inches and 13 treads at 10 inches, for a 130 inch total run.
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Formula
How it works: First, find how many risers you need by dividing the total floor-to-floor height by your target riser height and rounding to the nearest whole number. Then divide the total height by that number to get the actual rise per step. Treads always equal risers minus 1 because the top floor counts as the last tread. Multiply treads by your chosen tread depth for the total horizontal run.
Review and Methodology
This calculator runs locally in your browser. Inputs are converted into the units required by the formula, and the result is paired with supporting references so you can verify the method before using it for planning or estimates.
Worked Example
How to Calculate Stair Rise and Run
Stair design comes down to dividing a total height into equal, comfortable steps. Get this wrong and the stairs feel either steep and dangerous or shallow and tiring.
Start with the total floor-to-floor rise (finished floor to finished floor). Divide by a target riser height in the 7 to 7.75 inch range and round to the nearest whole number. Then divide the total rise by that whole number to get the actual riser height; this is what you frame.
Treads always equal risers minus one because the upper floor counts as the final landing. Multiply tread count by your tread depth (10 inches minimum under IRC) for the total horizontal run, which determines how much floor space the stair consumes.
The long-standing rule for comfort is 2R + T = 24 to 25 inches, where R is riser height and T is tread depth. Pairs like 7.5 in rise and 10 in tread (25 inches) or 7 in rise and 11 in tread (25 inches) feel natural to walk.
- IRC residential code: riser max 7.75 in, tread min 10 in, uniformity within 3/8 in
- IBC commercial code: riser max 7 in, tread min 11 in for public stairs
- Tread count = risers minus 1 (the upper floor is the last tread)
- Comfort rule: 2 x riser height + tread depth should equal 24 to 25 inches
- 8 ft ceiling needs 14-15 risers; 9 ft needs 16; 10 ft needs 17-18
Always check your local building code, since some jurisdictions amend the IRC. For framing the stringer cut, transfer the calculated rise and run directly to a framing square.
You can also calculate changes using our Square Footage Calculator, Concrete Yardage Calculator, Rectangle Volume Calculator or Asphalt Tonnage Calculator.
Common Stair Heights and Risers
Number of risers and rise per step for typical floor-to-floor heights using a 7.5 inch target riser.
| Floor-to-Floor | Total Rise (in) | Risers | Rise per Step | Code Status |
|---|---|---|---|---|
| 8 ft ceiling | 97 | 13 | 7.46 in | Pass |
| 8 ft 6 in | 103 | 14 | 7.36 in | Pass |
| 9 ft ceiling | 109 | 15 | 7.27 in | Pass |
| 9 ft 6 in | 115 | 15 | 7.67 in | Pass |
| 10 ft ceiling | 121 | 16 | 7.56 in | Pass |
Note: IRC R311.7.5 limits residential riser height to 7.75 inches. Always confirm with your local building department.
Frequently Asked Questions
How do you calculate the rise and run of stairs?
Divide the total floor-to-floor height by a target riser height (7 to 7.75 inches) and round to a whole number of risers. The actual rise per step is total height divided by risers. Tread count is risers minus 1; total run is treads times tread depth.
How to calculate run and rise of stairs?
Start with run (horizontal): tread depth times the number of treads, where treads equal risers minus 1. Then calculate rise (vertical): divide total floor-to-floor height by your number of risers. For 108 inches of total height, 14 risers gives 7.71 inch rise per step and 13 treads at 10 inches gives a 130 inch total run.
What is the IRC maximum riser height?
IRC R311.7.5 sets the maximum riser height for residential stairs at 7.75 inches and the minimum tread depth at 10 inches. Commercial stairs under IBC are stricter: 7 inch max riser and 11 inch minimum tread.
How many stairs do I need for an 8 foot ceiling?
An 8 ft ceiling typically gives about 97 inches of total floor-to-floor rise once joists and finish floors are added. That works out to 13 risers at 7.46 inches each and 12 treads, well within IRC limits.
What is the 2R plus T rule?
The 2R + T rule says twice the riser height plus the tread depth should total 24 to 25 inches for a comfortable stride. A 7.5 inch riser with 10 inch tread (25 inches) and a 7 inch riser with 11 inch tread (25 inches) both pass.
Can riser heights vary within a flight?
Per IRC, the variation between the largest and smallest riser in a single flight must not exceed 3/8 inch. Uniform risers prevent trips and falls. The same tolerance applies to tread depth.
Why is tread count always risers minus 1?
Because the upper floor surface acts as the final landing or tread. If you have 14 risers, you have 13 treads plus the floor at the top. Counting otherwise would double-count the destination.
How can I put this Stair Rise and Run Calculator on my blog or website?
Yes, the Stair Rise and Run Calculator is fully embeddable. Tap "Embed" above to configure appearance and copy the code. It is free to use, works on any platform (HTML, WordPress, CMS), and adjusts to any screen size automatically. Visit calculory.com/services/embed-calculators for the complete guide.
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