Stair Calculator (Metric)
Enter your total rise and a tread depth to get the number of steps, the riser height, total run, and stringer length for a straight stair.
What your result means
Number of risers is how many vertical steps you need, found by dividing total rise by a target near 19.1 cm and rounding. Riser height is the exact height of each step. Stringer length is the diagonal board the steps cut into. Most codes cap risers around 19.7 cm and want treads of at least 25.4 cm — check yours. Lay out the cuts with our board foot calculator for the lumber.
How to use this calculator
- Measure the total rise: finished floor to finished floor.
- Pick a tread depth, usually 10 to 27.9 cm.
- Read the number of risers and the exact riser height.
- Check the riser height falls in your code's range (often 7 to 19.7 cm).
- Use the stringer length to buy and lay out your stringer boards.
The formula
Dividing total rise by a comfortable ~19.1 cm target and rounding gives a whole number of risers; the exact height is total rise over that count. The stringer is the hypotenuse of the rise and total run.
Worked example
For a 274.3 cm total rise (a 2.7 m floor-to-floor) with 25.4 cm treads: 108 / 7.5 is 14.4, rounded to 14 risers at 19.6 cm each. That's 13 treads, a 330.2 cm run, and a stringer about 429.3 cm long.
Stair code rules of thumb
| Element | Typical requirement |
|---|---|
| Riser height | 7 - 19.7 cm (max varies) |
| Tread depth | 25.4 cm minimum (run) |
| Riser consistency | Within 3/20.3 cm across the flight |
| Headroom | 1.8 m 20.3 cm minimum |
| Handrail | 34 - 96.5 cm above nosing |
Tips & gotchas
- Keep every riser within 3/20.3 cm of the others — inconsistent steps are a trip hazard and a code fail.
- Deeper treads and shorter risers feel safer and more comfortable.
- Check your local code; riser and tread limits vary by jurisdiction.
- Account for finished floor thickness at top and bottom in your total rise.
- This is a straight-run estimate — winders and landings change the layout.
Frequently asked questions
How do I calculate stairs?
Divide total rise by about 19.1 cm and round for the number of risers, then divide total rise by that count for exact riser height. Treads are usually 10 to 27.9 cm.
What is a comfortable riser height?
Around 7 to 19.1 cm. Most codes cap risers near 19.7 cm; shorter risers with deeper treads feel safer.
How many steps for an 8-foot ceiling?
With finished floors, total rise is often around 105 to 276.9 cm, which works out to about 14 risers at roughly 7.5 to 19.7 cm each.
What is the stringer length?
The diagonal length of the board the steps are cut into — the hypotenuse of the total rise and total run. For a 2.7 m rise it's about 429.3 cm.
Do stairs have to meet code?
Yes. Riser height, tread depth, consistency, headroom, and handrails are all code-regulated. Confirm local rules before building.
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