Stair Calculator with Diagram (Metric)
Enter your total rise and available run to get risers, riser height, treads, and tread depth, with a stringer diagram to mark out the cuts.
What your result means
The calculator splits your rise into even risers near 19.1 cm, then divides your available run across the treads (one fewer than risers, since the top floor is the last step). Mark these onto the stringer with a framing square, and confirm the riser height and tread depth land within IRC limits before you cut.
How to use this calculator
- Measure total rise (height) and total available run (horizontal).
- Calculator picks ideal riser height (around 19.1 cm) and computes tread depth.
- Diagram shows stringer with calculated dimensions.
- Verify against local code (max riser 19.7 cm IRC).
- Cut stringer carefully - measure twice, cut once.
The formula
Divide the rise by 7.5 and round for the number of risers, then split the rise evenly across them for the actual riser height. Treads are one fewer than risers, and the tread depth is the run divided by the treads.
Worked example
Say you've got a 91.4 cm rise and 111.8 cm of run to work with. That's 5 risers at 18.3 cm each and 4 treads at 27.9 cm deep, which is a comfortable, code-friendly stair.
Stair anatomy & IRC limits
| Item | IRC limit |
|---|---|
| Max riser height | 19.7 cm |
| Min tread depth | 25.4 cm |
| Riser uniformity | within 3/20.3 cm |
| Min stair width | 91.4 cm |
| Handrail required | 4+ risers |
Tips & gotchas
- The stringer is the diagonal board that carries the treads and risers.
- Mark the notches with a framing square set to your rise and run.
- Max riser height per IRC is 19.7 cm; minimum tread depth is 10.
- All risers must be uniform within 3/20.3 cm or the stair feels wrong underfoot.
- A handrail is required once you have 4 or more risers.
Frequently asked questions
What is a stair stringer?
The diagonal cut board that supports the treads and risers.
How do I cut a stair stringer?
Mark the notches with a framing square at your rise and run, cut with a circular saw, and finish the inside corners with a handsaw.
What are the IRC stair requirements?
Max riser 19.7 cm, min tread 25.4 cm, min width 91.4 cm, all uniform within 3/20.3 cm.
How wide should stairs be?
91.4 cm minimum per IRC; 48 is more comfortable.
Do I need handrails?
Yes, once a stair has 4 or more risers, and on both sides if it's wider than 111.8 cm.
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