To calculate a staircase, divide the total height to be crossed by a target riser height of about 180 mm: you get the number of risers. Round it up to the nearest integer, then re-divide the total height by this number to get the exact height of each riser — it must be between 125 and 200 mm. Then deduct the tread depth with the Blondel rule: tread depth = 630 − (2 × riser height), keeping it between 255 and 355 mm. The number of treads is always equal to the number of risers minus one.
A concrete example: for a height of 2,750 mm, we obtain 2,750 ÷ 180 = 15.3, thus 15 risers of 183 mm, with a tread depth of 263 mm and a total run of 3,682 mm.
The calculator below will do the calculation for you and check compliance with the Quebec Building Code.
Stair Calculator
Workshop tool
Stair Calculator
We calculate the combinations in accordance with the Quebec Building Code, section 9.8, and the height of the staircase.
Only one field is required: There is no button to click — the calculation updates automatically as soon as you change a value, and the calculated value is automatically updated when you change a value.
Possible combinations
All options are compatible for your height. Click on a line to hold it. The drawing and detail below will update.
| risers | Height | Giron | Reduction | Confort |
|---|
Detail of the chosen option
Reference values. riser: 125 to 200 mm. Staircase: 255 to 355 mm according to CCQ 2020, 210 to 355 mm according to CCQ 2015. Minimum width: 860 mm. Minimum escape: 1,950 mm. Maximum height of a flight without landing: 3,700 mm. Blondel rule (comfort, non-regulatory): 2 × height + staircase between 600 and 630 mm. CCQ 2020 becomes mandatory for all new projects after October 17, 2026. These values are for a private staircase serving a dwelling; your municipality may impose additional requirements. This calculator provides a design estimate, not a construction plan.
How to read the results
The combination table lists all possible risers numbers for your height. For 2750 mm, there are nine risers numbers from 14 to 22, and three entries appear in the Comfort column:
- Optimal — dimensions comply with the Code and Blondel’s rule. That’s what we recommend.
- Hors Blondel — the staircase would be legal but steep or tiring to use.
- Too long — the backlash exceeds the length you have indicated.
Le regression is the length of the staircase on the floor, once laid, and is often the decisive constraint in a renovation.
The Five-Step Method
1. Measure the total height
From the floor finished from bottom to floor finished This is the most common mistake: forget the thickness of the floor covering, often 15 to 20 mm, which then shifts all the treads.
2. Find the number of risers
Divide the total height by 180 mm, a comfortable riser height, and round it to the nearest integer.For 2750 mm: 2750 ÷ 180 = 15.3, so 15 risers.
3. Calculate the exact height
Divide the total height by the number of risers: 2,750 ÷ 15 = 183 mm. The result should be between 125 and 200 mm. All risers must then be exactly the same.
4. Deduct the tread depth
Apply Blondel: 630 − (2 × 183) = 263 mm, to be maintained between 255 and 355 mm according to the 2020 QCQ. Verification: 366 + 263 = 629 mm, within comfort range.
5. Check the backlash
Multiply the number of staircase steps by the number of steps: 14 × 263 = 3,682 mm. This is the length of the staircase on the floor.If it exceeds the available space, upgrade to a winder staircase or add a landing.
The mistakes that cost the most
- Measure on rough floor. The final coating changes the height of the first or last step, and breaks the uniformity required by the Code.
- Forget the thickness of the walk in the calculation of stringer.
- Count as many loops as risers. There is always one ridge less, because the last riser ends directly on the floor.
- Neglecting the headroom. A perfectly calculated staircase on the ground can be unusable if the stairwell opening is too short: 1,950 mm of free height above each step is required.
- Ignore Blondel. Compliant does not mean comfortable. See our staircase standards in Quebec.
Frequently Asked Questions
How to calculate the number of treads of a staircase?
Divide the total height to be crossed by 180 mm and round to the nearest integer, then divide the total height by that number to get the exact height of each riser.
What is the Blondel formula?
2 × riser height + crotch should give between 600 and 630 mm. It validates the comfort of the stride, not compliance with the Code.
What is the difference between a walk and a giron?
The step is the piece on which the foot rests, and the tread depth is the useful horizontal distance between two consecutive stair nosing.
How many girons for 15 risers?
Fourteen. There is always one giron less than risers.
How long is a staircase to the floor?
The backlash is equal to the number of turns multiplied by the turn value, for 15 risers and a 263 mm turn: 14 × 263 = 3,682 mm.
A doubt about your measurements?
The theoretical calculation provides a basis, but a staircase is designed on real measurements: exact height between finished floors, width of the stairwell opening, access constraints.We take these measurements on site before each manufacture.
See also the price of a custom staircase, browse Our Staircases or Contact us to validate your project.
