Stair Calculator
Number of steps, exact riser height, total run and the Blondel comfort value.
Results
Quantity
15
Height
18.00
cm
Length
392.0
cm
Length
64.00
cm
What this tool does
The total height rarely divides evenly by an ideal riser, so the practical method is to round to a whole number of steps and then recalculate the riser exactly. Every riser in a flight must be the same height — an odd one out is a trip hazard.
Formula
n = round(height ÷ ideal mirror) ; mirror = height ÷ n
Variables
| Symbol | Meaning | Unit |
|---|---|---|
h | Height | cm |
ri | Height | cm |
go | Depth | cm |
N | Quantity | — |
RH | Height | cm |
RUN | Length | cm |
BL | Length | cm |
Worked example
- Height270 cm
- Height17.5 cm
- Depth28 cm
- Quantity15
- Height18.00 cm
- Length392.0 cm
- Length64.00 cm
Limitations
- For work that must comply with a standard or be signed off, check the result against the applicable code and have it reviewed by a qualified engineer.
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.
Frequently asked questions
What is the last figure, the "blondel" value?
It is twice the riser plus the going, a comfort rule that has been used for centuries. Comfortable stairs usually land between 60 cm and 65 cm on this measure. It is a rule of thumb, not a regulation: your national building code sets the legal limits on riser height and tread depth.