Stair Calculator
Calculate riser count, tread count and practical stair dimensions.
Project details
Enter your measurements below.
Stair math can make risers equal; it cannot make a stair code-compliant
The essential stair problem is dividing the finished floor-to-floor rise into equal risers. An initial target riser height suggests a whole riser count; the actual riser is then recalculated so every step is equal. Tread count and horizontal run follow from that geometry. This calculator is useful for planning space and checking dimensions, but stairs are safety-critical. Headroom, landings, nosings, guards, handrails and maximum/minimum dimensions must be verified against the applicable requirements before construction.
Use finished-floor to finished-floor height, including planned finish thicknesses.
The final riser height is recalculated after choosing a whole number of risers.
Do not build directly from calculator output without checking all applicable stair requirements.
How to use the Stair Calculator
- Measure the total vertical rise from lower finished floor to upper finished floor.
- Enter a target or maximum riser value only as a planning input consistent with the applicable project requirements.
- Choose the whole riser count, then divide the total rise by that count to obtain an equal actual riser height.
- Use the appropriate tread count and depth to estimate horizontal run, then verify headroom, landings, handrails/guards and all dimensional limits.
Why the actual riser changes
A stair cannot have a fraction of a riser. Once the count becomes a whole number, dividing the exact total rise again produces the equal finished riser height.
Use the geometry to test whether the stair fits
Compare total run and rise with the available opening, but treat that as layout planning only. Final stair design still needs a complete compliance and construction check.
Worked example: 105 in total rise
- Finished rise
- 105 in
- Planning target
- 7.5 in
- Riser count
- 105 ÷ 7.5 = 14
- Actual riser
- 7.5 in
Fourteen equal risers fit the entered rise exactly in this simplified example. The number of treads and total run then depend on the stair arrangement and tread depth, which must satisfy the applicable requirements.
Practical planning tips
Re-measure after accounting for flooring thickness at both levels; a finish change can make the top or bottom riser uneven.
Check headroom early, not after the tread/run geometry is finalized.
Keep straight flights, winders and landings as distinct design conditions.
Treat stringer sizing, connections and openings as structural/construction details outside the geometry calculator.
Common mistakes to avoid
Measuring subfloor-to-subfloor when finished floor thicknesses differ.
Rounding individual riser heights independently instead of dividing the full rise into equal risers.
Assuming a comfortable-looking riser/tread pair automatically meets local code.
Ignoring headroom, landings, handrail and guard requirements because the rise/run math works.
Stair Calculator FAQs
Why must all risers be equal?+
Uneven risers create a trip hazard and are tightly controlled by building requirements. The calculator therefore recalculates one equal riser height from the whole riser count.
How many treads are there compared with risers?+
For a typical straight stair between floors, there is often one fewer tread surface than risers because the upper floor serves as the final landing, but stair configuration can differ.
Can I use a target riser from the calculator as a code limit?+
No. Use limits from the applicable local requirements and project design.
Does this calculate stringers?+
No. It calculates basic stair geometry, not structural stringer sizing, connections or code compliance.