How the stair calculation works
Every set of stairs comes down to one measurement: the total rise, which is the vertical distance from the finished floor at the bottom to the finished floor at the top. Everything else follows from it. You pick the tallest riser you are happy with, divide the total rise by that number, and round up to a whole number of steps. Then you divide the total rise by that whole number again to get the real riser height, so every step is identical.
For example, a basement with 108 inches from slab to main floor, and a 7 1/4 inch riser limit, gives 14.9 steps. You cannot build 14.9 steps, so you round up to 15 risers, and each one is exactly 7 3/16 inches. Because the top step is the floor itself, 15 risers means 14 treads.
Measure total rise the right way
Measure to the finished surfaces, not the framing. If the bottom will get a 3/4 inch hardwood tread over a slab, or the top floor still needs underlay and flooring, those thicknesses change your total. The most common mistake we see in DIY stairs is a first step that comes out a half inch shorter or taller than the rest because someone forgot the flooring. A variation of more than 3/16 inch (about 5 mm) between steps is a real trip hazard, and it is also what an inspector checks first.
Canadian code limits for residential stairs
The National Building Code of Canada (Part 9) sets the baseline for stairs inside a house, and provinces adopt it with their own tweaks. The figures below apply to private stairs in a dwelling. Check with your municipality before you cut anything, especially for exterior steps or any stair that serves more than one unit.
| Item | Typical dwelling limit |
|---|---|
| Riser height | 125 mm to 200 mm (about 5" to 7 7/8") |
| Tread run | 210 mm minimum (about 8 1/4"), 355 mm maximum |
| Tread depth with nosing | 235 mm minimum (about 9 1/4") |
| Stair width | 860 mm minimum (about 34") |
| Headroom | 1.95 m minimum (about 6'5") |
| Handrail height | 865 mm to 965 mm |
Ontario, British Columbia, Alberta and Quebec publish their own building codes that follow the national one closely but not word for word, so treat this table as a planning guide and the local code as the final answer.
Common stair layouts by total rise
These figures assume a 7 inch target riser and a 10 inch tread run. Your numbers will shift slightly with a different run.
| Total rise | Risers | Riser height | Treads | Total run |
|---|---|---|---|---|
| 30" | 5 | 6" | 4 | 40" |
| 36" | 6 | 6" | 5 | 50" |
| 48" | 7 | 6 27/32" | 6 | 60" |
| 60" | 9 | 6 21/32" | 8 | 80" |
| 96" | 14 | 6 27/32" | 13 | 130" |
| 108" | 16 | 6 3/4" | 15 | 150" |
| 120" | 18 | 6 21/32" | 17 | 170" |
Cutting the stringers
The stringer length the calculator gives is the long edge of the cut, which is the hypotenuse of the stair triangle. Add a little extra for the plumb cut at the top and the bottom, and buy your stock longer than the number shows. For a typical deck or basement stair, 2x12 stringers work well. You need at least 3 1/2 inches of uncut wood left below the notches, and most builders set stringers 12 to 16 inches apart, closer for wide treads or heavier use.
Mark the first notch with a framing square set to your riser and run, using stair gauges so the settings do not drift. After the first stringer is cut, use it as a template for the rest. When you set the stringer on the bottom, remember to trim off one tread thickness from the bottom riser, otherwise the first step ends up too tall once the tread goes on.
Exterior steps and deck stairs
Deck stairs follow the same maths but add two wrinkles: the ground at the bottom is rarely level, and the top is measured to the deck surface, not the joist. Treat the landing pad as the bottom of your total rise, set it first, and then measure up. In cold regions, a stair landing sitting on gravel can heave with the frost, so a concrete pad on compacted base keeps the first riser from changing height over winter. If you are working on a deck, our lumber and framing calculators will help with the rest of the materials list.
Stairs, ramps and railings together
If the same entrance needs a ramp for accessibility, a standard slope is much shallower than stairs, and our ramp calculator sizes it from the same total rise. Balusters on the open side must keep gaps small enough that a 100 mm ball cannot pass through, which the baluster spacing calculator works out for you.
Mistakes worth avoiding
Do not mix riser heights to make the numbers work. Do not forget that tread nosing is counted separately from the run. Do not measure the total rise from the subfloor when finished flooring is coming. And do not assume an old house meets modern code; older stairs are often steeper, and renovations that touch them may trigger an upgrade, so ask your building department first.
Frequently asked questions
How do I calculate stairs?
Measure the total rise from finished floor to finished floor, divide by your maximum riser height, and round up to a whole number of risers. Divide the total rise by that number to get the exact riser height. The number of treads is always one fewer than the number of risers.
What is the maximum riser height for stairs in Canada?
For private stairs in a dwelling, the National Building Code of Canada allows a riser up to 200 mm, which is about 7 7/8 inches. Provincial codes can differ slightly, so confirm with your local building department.
What is the minimum tread depth for stairs in Canada?
Residential treads need a run of at least 210 mm (8 1/4 inches) and an overall tread depth of at least 235 mm (9 1/4 inches) including the nosing.
How do I find the stringer length?
Multiply the number of treads by the tread run to get the total horizontal run, then use the Pythagorean theorem with the total rise. The calculator above does this for you and adds the angle.
How many stairs do I need for 8 feet of rise?
Eight feet is 96 inches. With a 7 inch maximum riser you need 14 risers, each about 6 27/32 inches high, and 13 treads.
Can I use this for deck stairs?
Yes. Use the distance from the top of the deck surface to the finished landing as the total rise, and use a tread run of 10 inches or more.
Related calculators
Estimates only. See our disclaimer and how we calculate.