Staircase Calculator
Divide the floor-to-floor height by the target riser height and round up to get the riser count. A 9 ft rise with 7 inch target risers gives 16 risers at 6.75 inches, 15 treads, and a stringer of about 17.1 ft.
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Formula
- Total rise = Floor-to-floor height x 12 inches
- Number of risers = Total rise / target riser height, rounded up
- Actual riser = Total rise / number of risers
- Treads = Risers - 1
- Total run = Treads x tread depth
- Stringer = square root of (rise squared + run squared)
Worked Example
| Input | Value |
|---|---|
| Floor height | 9 ft = 108 in |
| Target riser | 7 in |
| Risers | 16 |
| Actual riser | 6.75 in |
| Treads | 15 |
| Tread depth | 10.5 in |
| Total run | 13.13 ft |
| Stringer | 17.09 ft |
| IRC check | Pass |
Frequently Asked Questions
What is the maximum stair riser height?
IRC 2021 R311.7.4 allows a maximum riser of 7.75 inches for residential stairs.
What is the minimum tread depth?
IRC 2021 requires a minimum tread depth of 10 inches.
Why is there one fewer tread than riser?
The upper floor surface acts as the final landing, so a flight always has one more riser than it has treads.
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Estimates only. Quantities follow recognised standards (ACI 318, CRSI, IRC 2021, IS-1077, PBQS); actual site consumption varies with workmanship, wastage and detailing. Confirm with a licensed engineer before ordering.