Steps that are all the same height
A comfortable, safe staircase has every step the same height and depth, so feet find a rhythm without thinking. The trick is to start from the total rise, the exact height from one finished floor to the next, and divide it evenly.
This stair calculator works out how many risers you need so that none is taller than the limit you set, the exact height of each riser, the number of treads, the total run the stairs take up, and the approximate stringer length and angle.
How to use it
- Measure the total rise from the top of the lower finished floor to the top of the upper finished floor.
- Enter the tallest riser your local building code allows, and the tread depth you plan to use.
- Read the number of risers and treads, the exact riser height and the total run.
- Use the stringer length to choose timber, adding enough for the cuts at the top and bottom.
Measure the rise with the final floor finishes in mind. A thick floor covering added later changes the height of the top or bottom step.
The stair formulas
risers = total rise ÷ tallest riser, rounded up
riser height = total rise ÷ risers
treads = risers − 1 (the upper floor is the last step)
total run = treads × tread depth; stringer ≈ √(rise² + run²)There is always one more riser than tread in a straight flight, because you step up onto the upper floor itself. A long used rule of thumb for comfort says that twice the riser plus the tread should come to about 24 to 25 inches; the calculator shows that figure for your design.
Worked example: a 108 inch rise
- 108 ÷ 7.75 = 13.94, rounded up to 14 risers
- Each riser: 108 ÷ 14 = 7.71 in
- 13 treads × 10 in = 130 in of total run (10.83 ft)
- Stringer: √(108² + 130²) ≈ 169 in
This staircase needs 14 risers, 13 treads, each riser 7.71 in high, and 130 in of floor space for the run. Twice the riser plus the tread is about 25.4 in, so the stairs will feel natural to climb.
Common floor heights
| Total rise | Steps | Riser height | Total run |
|---|---|---|---|
| 96 in | 13 risers, 12 treads | 7.38 in | 120 in (10 ft) |
| 102 in | 14 risers, 13 treads | 7.29 in | 130 in (10.83 ft) |
| 108 in | 14 risers, 13 treads | 7.71 in | 130 in (10.83 ft) |
| 114 in | 15 risers, 14 treads | 7.6 in | 140 in (11.67 ft) |
| 120 in | 16 risers, 15 treads | 7.5 in | 150 in (12.5 ft) |
Building codes also set rules for headroom, handrails, landings and the smallest tread depth. Rules differ from place to place, so check them before you cut.
Related tools
- For the angle of a sloped surface, try the slope calculator.
- For roofs, the roof pitch calculator works with rise and run in the same way.
- For a stair stringer as a right triangle, the triangle calculator solves every side and angle.
Frequently asked questions
How do I calculate the number of stairs?
Divide the total rise, floor to floor, by the tallest riser height allowed, and round up to a whole number. That gives the number of risers. For a 108 inch rise and a 7.75 inch limit, 108 ÷ 7.75 is 13.94, so you need 14 risers and 13 treads.
Why is there one fewer tread than risers?
In a straight staircase, the last step up lands on the upper floor itself, which acts as the top tread. So 14 risers need only 13 separate treads. The total run of the stairs is the number of treads times the tread depth, not the number of risers.
What is a comfortable riser and tread size?
A long used rule of thumb says twice the riser height plus the tread depth should be about 24 to 25 inches, roughly a normal walking stride. A 7 inch riser with an 11 inch tread fits it well. Local building codes set the limits, so check those first.
How long should a stair stringer be?
Roughly the diagonal of the rise and the run: the square root of rise squared plus run squared. For a 108 inch rise and 130 inch run, that is about 169 inches. Buy timber longer than this, since the cuts at the top and bottom need extra length.
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