Stair Calculator
Steps, riser height, run, and stringer length from total rise.
What it does
Comfortable stairs divide the total rise into even risers near seven inches, because one tall step among short ones trips feet that memorized the rhythm. Rounding up guarantees every riser stays at or under the max.
The tool above takes total rise with tread depth in either system. It returns step count, exact riser height, total run, and stringer length point to point.
Codes cap risers near 7.75 inches with ten inch minimum treads in US residential work, and comfort bands run slightly tighter. Local rules always win over rules of thumb.
Landings split long runs for rest and safety. Steep basement stairs trade comfort for footprint, which the same math still sizes honestly.
How to use
- Switch the unit system first: imperial for inches, metric for cm.
- Measure total rise floor to finished floor.
- Pick tread depth: minimum or comfortable.
- Cut stringers to the point to point length plus landing overlap.
Formula
- 7 in / 18 cm
- Riser target keeping steps comfortable.
- ceil
- Round steps up so risers never exceed the max.
- hypotenuse
- Stringer diagonal across total rise and run.
Headroom needs about 80 inches above nosings along the whole run. Low basements fail headroom before riser math matters.
Worked example
Example: 42 in rise, 11 in treads
Deck 42 inches above grade, comfortable treads.
- Steps: 42 / 7 = 6 exactly.
- Riser: 42 / 6 = 7 in each.
- Run: 6 x 11 = 66 in.
- Stringer: sqrt(42² + 66²) = sqrt(6120) = 78.2 in point to point.
Reference table
| Rise | Steps | Riser |
|---|---|---|
| 28 in | 4 | 7 in |
| 35 in | 5 | 7 in |
| 42 in | 6 | 7 in |
| 48 in | 7 | 6.86 in |
| 60 in | 9 | 6.67 in |
Limits
- Straight runs assumed. Winders and landings need layout.
- Tread nosing and landing overlap excluded.
- Codes vary by place and stair type.
- Headroom checked separately, not computed.
Common mistakes
- Uneven risers from rounding down instead of up.
- Measuring to subfloor instead of finished floor.
- Forgetting landing depth in tight spaces.
- Cutting stringers exact with no overlap margin.
- Ignoring headroom until framing stands.
Try it yourself
Quick checks. Answers sit tucked under each question.
36 in rise. Steps and riser?
Ceil(36/7) = 6 steps. Riser 36/6 = 6 in.
Run with 11 in treads?
6 x 11 = 66 in.
Questions
How tall should each step be?
Near 7 inches. Codes cap near 7.75; comfort prefers 7 or under.
How deep should treads be?
Eleven inches comfortable, ten minimum. Nosing adds about an inch.
Why round steps up?
Rounding down overshoots the max riser. Up keeps every step legal.
What is stair stringer length?
The diagonal board span: hypotenuse of total rise and run.
How much headroom do stairs need?
About 80 inches above every nosing along the run.
Do I need a landing?
Long runs and direction changes want one. Codes set maximum rises between landings.