Free Tool
Stair Stringer Calculator
Enter the total rise from finished floor to finished floor. The calculator finds the number of risers, the riser height, the tread count, the total run and the stringer length, and checks them against the Ontario Building Code limits for a private stair.
Stair Stringer Calculator
Result
Layout
Code checks
Other options for the same rise
Preliminary planning only. This tool does not replace the drawings. The designer or engineer of record and the building permit set govern every size, span and detail.
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https://timberrframing.com/api/tools/stair-stringer-calculator?rise_ft=8&rise_in=10&run_mm=280
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How the calculator works
- Risers. The total rise divided by 200 mm, rounded up. The riser height is the total rise divided by that number of risers.
- Treads and run. The treads are one fewer than the risers. The total run is the treads times the run per tread, with the run measured nosing to nosing.
- Stringer length. The straight line along the nosings, the square root of the total rise squared plus the total run squared. It is the line along the nosings, not the cut length of the board. Add for the plumb and level cuts and for the board you start from.
- First and last riser. The bottom riser is cut shorter by the tread thickness, and the top is set to the framing, so that every finished riser comes out equal once treads are on. The thickness field shows that adjustment.
- Limits checked. Table 9.8.4.1. (rise 125 to 200 mm and run 255 to 355 mm for private stairs), Article 9.8.4.2. (tread depth not less than the run and not more than 25 mm over it), Article 9.8.4.4. (riser tolerance 5 mm adjacent and 10 mm overall), Article 9.8.3.3. (a flight rises no more than 3.7 m), Article 9.8.2.1. (stair width at least 860 mm) and Article 9.8.2.2. (headroom at least 1 950 mm).
- Private stairs only. Public, service, and attic stairs have different limits in the same table and are not covered. Winders, tapered treads, spiral stairs, landings, guards and handrails are not calculated.
This tool is for preliminary planning. The designer or engineer of record and the building permit set govern.
Frequently asked questions
What are the rise and run limits for a private stair in Ontario?
Table 9.8.4.1. of the 2024 Ontario Building Code gives a private stair a rise of 125 to 200 mm and a run of 255 to 355 mm for rectangular treads. Private stairs are interior stairs within a house with a secondary suite or an individual dwelling unit, and the exterior stairs serving them.
How is the number of risers decided?
Divide the total rise by the largest rise you are allowed to use, 200 mm, and round up to a whole number of risers. Then divide the total rise by that number to get the actual riser height. All risers in a flight must be equal within 5 mm between adjacent treads and 10 mm between the tallest and the shortest (Article 9.8.4.4.).
How many treads are there?
One fewer than the number of risers, because the floor at the top acts as the last tread. A flight of 14 risers has 13 treads.
How deep is the tread compared with the run?
A rectangular tread must be at least as deep as its run and not more than 25 mm deeper (Article 9.8.4.2.). Where the tread overlaps the one below, the depth is the run plus the nosing.
How much headroom does a stair need?
Over a stair serving a single dwelling unit or a house with a secondary suite, the clear height is not less than 1 950 mm, measured vertically from a line tangent to the nosings (Article 9.8.2.2.). Under beams and ducting in secondary suites the minimum is 1 850 mm.
When is a landing needed?
A single flight may not rise more than 3.7 m (Article 9.8.3.3.). A landing is needed at the top and bottom of each flight and where a door opens onto the stair, with the exceptions in Article 9.8.6.2.
Is this a quote?
No. It is a planning tool. Contact us with your plans and we will arrange a free site visit.
For the floor opening, landings and guards, read Stair Framing in Ontario.
Related: Stair framing, Basement framing, Home addition framing.
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