Stair Riser Calculator
Enter your total rise and compare every workable riser height and step count side by side, with the IRC 7¾″ maximum checked for each option.
| Steps | Riser Height | Comfort* | |
|---|---|---|---|
| 14 | 7.71" (7 11/16") | 18.2" | Recommended |
| 15 | 7.2" (7 3/16") | 17.7" | |
| 16 | 6.75" (6 3/4") | 17.3" | |
| 17 | 6.35" (6 5/16") | 16.9" | |
| 18 | 6.0" (6") | 16.5" |
*Comfort = riser + 10.5" tread. The sweet spot is 17"–18".
How riser height is calculated
Riser height is total rise divided by the number of steps — the whole game is picking a step count that lands the riser where you want it. Code gives you a ceiling: 7¾" maximum for residential stairs (IRC R311.7.5.1). Comfort gives you a target: most people find 7" to 7.5" risers the easiest to climb.
For a 108" floor-to-floor height: 108 ÷ 14 = 7.71" (legal, steep side), 108 ÷ 15 = 7.2" (comfortable, one more step of total run), 108 ÷ 16 = 6.75" (shallow, good for aging-in-place). Each added step trades about half an inch of riser for another tread's worth of horizontal run — that is the real decision this table lets you make.
Getting equal risers in practice
- The 3/8" rule: the tallest and shortest riser may differ by no more than 3/8" (IRC R311.7.5.1). Divide total rise by step count and mark every notch from the same reference edge — never cumulative tape measurements.
- Drop the bottom riser by one tread thickness. Skipping this makes the first step taller than the rest by exactly the tread thickness — a code violation and the classic DIY mistake.
- Check both landings: finished flooring thickness at top or bottom changes your effective total rise. Measure finished surface to finished surface.
- Uneven ground on decks: measure total rise at the stair landing location, not at the deck rim.
Frequently asked questions
- What is the ideal stair riser height?
- Around 7"–7.5". The IRC allows up to 7¾" (R311.7.5.1), but risers near 7" feel more comfortable, especially paired with a tread that puts rise + run between 17" and 18".
- What is the maximum riser height by code?
- 7¾" (7.75") for residential stairs under IRC R311.7.5.1. Commercial stairs under the IBC are stricter: 7" maximum (IBC 1011.5.2). Local amendments can be stricter still.
- How do I calculate riser height?
- Divide total rise by the number of steps. If the result exceeds 7.75", add a step and divide again. For a 60" rise: 60 ÷ 8 = 7.5" per riser.
- Why do all risers have to be the same height?
- The IRC allows at most 3/8" of variation between the tallest and shortest riser (R311.7.5.1). An odd riser mid-flight is a trip hazard and one of the most common inspection failures.