How to use it
- Measure the total rise from the finished floor below to the finished floor above, and type it in Total rise, floor to floor.
- If the stair has a set length, type it in Horizontal run available. Otherwise leave it empty.
- Read Number of risers, Height of each riser and Depth of each tread.
- Then check the Check against the regulation line, and the Run available line if you typed a run.
How the riser and tread are chosen
The number of risers must be high enough that no riser is above the limit, and low enough that no tread is below the minimum tread. The design takes the larger of the two counts, so both limits are met, then sets the tread so that 2 × riser + tread is 63 cm, the middle of the 60 to 66 cm comfort band.
The rule 2 × riser + tread is Blondel's rule. The Wikipedia article on stairs gives it as: twice the riser plus the tread equals the step length, a rule first set down by Nicolas-François Blondel in his course of architecture in the 1670s and 1680s. The 63 cm figure with its band of ± 3 cm comes from the German DGUV step-length rule.
risers = larger of [rise ÷ highest riser] and [2 × rise ÷ (63 cm − smallest tread)], rounded up
riser = rise ÷ risers
tread = 63 cm − 2 × riser
going = (risers − 1) × tread
angle = arctan(riser ÷ tread)
stringer = √(rise² + going²)The limits
The guide takes two limits from DIN 18065, the German standard for stairs in buildings, as the German Wikipedia article on stairs states them: a riser of at most 19 cm, and a tread of at least 26 cm. The step-length rule, tread + 2 × riser = 63 cm ± 3 cm, comes from the German statutory accident insurance (DGUV), which gives the band of 60 to 66 cm.
This is a comfort guide, not a building code. Building rules differ by country, state and municipality and decide what is allowed for your stair, so check them with your local building authority or an architect.
What this calculator does not include
- Landings, the headroom over the stair, handrails and guards, and the width of the flight.
- Winders, spiral stairs and stairs with a turn. Each flight here is straight.
- The nosing (the overhang of the tread), which some codes allow; check it on the drawing.
Worked example: a rise of 3.00 m
The rise limit gives 3.00 ÷ 0.19 = 15.79, so 16 risers. The tread limit gives 2 × 3.00 ÷ (0.63 − 0.26) = 16.22, so 17. The larger count, 17, is used.
Each riser is 3.00 ÷ 17 = 0.17647 m, shown as 17.6 cm, and each tread is 63 cm − 2 × 17.647 cm = 27.71 cm, shown as 27.7 cm. The going is 16 × 27.706 cm = 4.43 m, the angle is about 32.5° and the stringer is √(3.00² + 4.43²) = 5.35 m.
| Riser | Height above the floor | Distance from the bottom | |
|---|---|---|---|
| First | 1 | 17.6 cm | 0.0 cm |
| Last | 17 | 300.0 cm | 443.3 cm |
Frequently asked questions
What riser and tread are comfortable for a staircase?
Use the comfort rule: twice the riser plus the tread is about 63 cm. The German figures this guide uses allow a riser of at most 19 cm and a tread of at least 26 cm, with 2 × riser + tread between 60 and 66 cm.
Why does the number of risers change when I change the rise?
The riser cannot be above the limit, so a taller rise needs more risers. Each extra riser lowers the riser height and so raises the tread that the comfort rule allows.
What is the going of a stair?
The going is the horizontal length the flight covers, from the first riser to the top one. It is the number of treads between the floors times the tread depth; it is not the length of the stair itself.
Is this calculator a building code?
No. It is a comfort guide built on German figures, not a building code. Ask your local building authority or an architect which rules apply to your building, because they may set other limits.
What does the run check mean?
If you type the length the stair may take, the calculator checks whether the flight fits it. A flight that does not fit needs a landing, a turn or a shorter rise per flight.
Does the tool store what I enter?
No. The calculation runs in your browser and nothing you type is sent to us or stored.
Sources
- Wikipedia (German): Treppe, the DIN 18065 limits and the DGUV step-length rule
- Wikipedia: Stairs (the 2 × riser + tread rule)
Figures and text last checked on Friday, November 13, 2026.