Stair Calculator
Turn a total rise (floor-to-floor height) into the number of steps, the exact riser height and tread depth, the stringer length, and a check against the National Building Code of Canada's residential riser and tread limits.
13 risers · 12 treads
Riser height: 192.3 mm Tread depth: 255 mm Stringer: 3,951.4 mm at 39.2°
✓ Meets NBC/CNB residential riser (125–200 mm) and tread (≥ 235 mm) limits.
Within the classic "rise + run = 17–18 in" comfort formula. Total run: 3,060 mm.
Code limits per the National Building Code of Canada (residential, harmonized into BC/ON building codes): max riser 200 mm, min riser 125 mm, min tread 235 mm. Always confirm with your local building department before construction. How we calculate →
How do you calculate the number of stairs from total rise?
Divide the total rise (the vertical distance from one floor to the next, plancher à plancher) by the maximum riser height allowed — 200 mm under the National Building Code of Canada for residential stairs — and round up. A 2,500 mm total rise needs at least ⌈2,500 ÷ 200⌉ = 13 risers, which then splits the rise evenly into 13 steps of about 192.3 mm each.
The number of treads is one less than the number of risers, since the top floor level serves as the final "step." 13 risers means 12 treads in the flight.
What are Canada's building code limits for stairs?
The National Building Code of Canada sets residential riser height between 125 mm and 200 mm, and a minimum tread (run) depth of 235 mm, measured without counting any nosing overhang. These limits are harmonized into the provincial codes (BC, Ontario and others) with only minor local amendments, which is why they're the standard reference for a new residential stair.
The 17-18 inch comfort rule
Beyond code minimums, stair builders often aim for riser + tread between 17 and 18 inches (about 432–457 mm) for a comfortable stride — a stair can be fully code-compliant and still feel awkward if it sits outside that range. The calculator flags both the code check and the comfort check separately, since they're not the same test.
How do you find the stringer length?
The stringer (the diagonal board the treads attach to) spans the hypotenuse of a right triangle formed by the total rise and the total run (number of treads × tread depth). For 13 risers at 192.3 mm and 12 treads at 255 mm (total run 3,060 mm) over a 2,500 mm rise, the stringer length is √(2,500² + 3,060²) ≈ 3,951 mm — before adding material for the board's own thickness and any overhang.
Frequently asked questions
How many stairs do I need for a 2500 mm rise?
At the code maximum riser of 200 mm, you need at least ⌈2500 ÷ 200⌉ = 13 risers, giving an actual riser height of about 192.3 mm (within the 125–200 mm code range) and 12 treads. Enter your exact rise above for your own numbers.
What is the maximum riser height allowed in Canada?
Under the National Building Code of Canada, a residential riser must be no taller than 200 mm and no shorter than 125 mm. These limits carry through into provincial codes like the BC Building Code and Ontario Building Code with only minor local amendments.
What is the minimum tread depth for stairs in Canada?
The National Building Code of Canada sets a minimum tread (run) depth of 235 mm for residential stairs, measured excluding any nosing overhang. A tread shallower than that is considered a code violation regardless of how comfortable it might feel.
How do you calculate stringer length for stairs?
Stringer length is the hypotenuse of the total rise and total run: √(rise² + run²). For a 2,500 mm rise with 12 treads of 255 mm each (3,060 mm total run), that's √(2,500² + 3,060²) ≈ 3,951 mm, before allowing extra material for the board thickness and top/bottom cuts.
What is the 17-18 inch rule for stairs?
It's a comfort guideline (not a code requirement): the riser height plus the tread depth should add up to roughly 17 to 18 inches (432–457 mm). A stair with a 192 mm riser and 255 mm tread sums to about 447 mm — inside that comfortable range.
Researched & verified by the Calcuris Data & Research Team. How we build and check our tools →