🪜 Stair Calculator
By ToolNimba Construction Team · Reviewed by ToolNimba Editorial Review, construction and DIY content · Updated 2026-06-19
This stair calculator is a planning aid, not a substitute for your local building code or a qualified builder. Code limits on riser height, tread depth, headroom, handrails and landings vary by jurisdiction and by stair type. Always verify your design against the rules that apply where you build, and have load-bearing work checked by a professional.
The number of steps equals the number of risers. A flight has one fewer tread than risers, because the top step lands on the upper floor. Recommended tread uses the comfort rule 2 x riser + tread = 25 in. Always confirm against your local building code.
This stair calculator turns a floor-to-floor height into a buildable flight of stairs. Enter the total rise (the vertical distance from one finished floor to the next) and the step height you are aiming for (around 7 inches is comfortable). It works out the number of steps, the exact riser height, a recommended tread depth, and the total horizontal run, so you can lay out a stringer with confidence.
What is the Stair Calculator?
A staircase is defined by two repeating measurements: the riser (the vertical height of each step) and the tread or going (the horizontal depth you step on). The total rise is fixed by your building, the floor-to-floor height, so the design choice is how many steps to divide that rise into. More steps means a shorter, gentler riser; fewer steps means a taller, steeper one. The calculator divides your total rise by the target step height and rounds to a whole number, because every step in a flight must be the same height.
Once the number of steps is set, the actual riser height is simply the total rise divided by that number. This is almost never exactly your target, and that is fine: what matters is that all risers are equal to within a small tolerance (codes typically allow about 3/8 inch of variation across a flight). The recommended tread comes from a long-standing comfort rule, 2 x riser + tread = about 25 inches, which keeps the relationship between step height and depth natural for the human stride. A tall riser pairs with a shallow tread, a short riser with a deeper one.
The number of treads is one fewer than the number of risers, because the top riser lands you on the upper floor, which acts as the final tread. The total run is the number of treads multiplied by the tread depth, and it tells you how much floor space the stairs will eat up. Knowing the run early matters: a flight that is too long may not fit the opening, and you may need a landing, a turn, or a steeper design to make it work.
When to use it
- Planning a new staircase between two floors and checking it will physically fit the available run.
- Cutting a stair stringer: the riser height and tread depth are exactly the marks you scribe with a framing square.
- Checking that an existing or proposed stair meets common code limits on riser height and tread depth.
- Comparing two layouts, for example 14 versus 15 steps, to balance comfort against the floor space used.
How to use the Stair Calculator
- Pick your unit: inches or centimeters.
- Enter the total rise, the finished floor-to-floor height.
- Enter the target step height you are aiming for, about 7 in (18 cm) is a comfortable default.
- Read off the number of steps, the exact riser height, the recommended tread, and the total run, with code flags shown beside each result.
Formula & method
Worked examples
A floor-to-floor height of 108 in (9 ft), aiming for a 7 in step.
- number of steps = round(108 / 7) = round(15.43) = 15
- actual riser = 108 / 15 = 7.20 in
- recommended tread = 25 - 2 x 7.20 = 10.60 in
- number of treads = 15 - 1 = 14
- total run = 14 x 10.60 = 148.40 in (about 12 ft 4 in)
Result: 15 steps, riser 7.20 in, tread 10.60 in, total run about 148.4 in
A floor-to-floor height of 120 in (10 ft), aiming for a 7 in step.
- number of steps = round(120 / 7) = round(17.14) = 17
- actual riser = 120 / 17 = 7.06 in
- recommended tread = 25 - 2 x 7.0588 = 10.8824 in (shown as 10.88)
- number of treads = 17 - 1 = 16
- total run = 16 x 10.8824 = 174.12 in (about 14 ft 6 in)
Result: 17 steps, riser 7.06 in, tread 10.88 in, total run about 174.1 in
Common residential stair limits (US IRC as a typical guide, always confirm locally)
| Dimension | Typical limit | Notes |
|---|---|---|
| Maximum riser height | 7 3/4 in (19.7 cm) | Measured vertically between treads |
| Minimum tread depth | 10 in (25.4 cm) | Nosing to nosing, excluding overhang |
| Comfort rule | 2R + T = 24 to 25 in | Riser plus riser plus tread |
| Riser variation in a flight | about 3/8 in (1 cm) | Largest minus smallest riser |
| Minimum headroom | 6 ft 8 in (203 cm) | Measured plumb from the nosing line |
Suggested steps and riser height by total rise (target 7 in step)
| Total rise | Steps | Riser height | Treads |
|---|---|---|---|
| 96 in (8 ft) | 14 | 6.86 in | 13 |
| 102 in (8.5 ft) | 15 | 6.80 in | 14 |
| 108 in (9 ft) | 15 | 7.20 in | 14 |
| 114 in (9.5 ft) | 16 | 7.13 in | 15 |
| 120 in (10 ft) | 17 | 7.06 in | 16 |
Common mistakes to avoid
- Counting risers and treads as the same. They are not. A flight always has one fewer tread than risers, because the top riser brings you up to the upper floor, which serves as the last tread. Cutting a stringer with the wrong tread count is a common, costly slip.
- Using the target step height as the actual riser. Your 7 in target almost never divides the total rise evenly. The real riser is total rise divided by the whole number of steps, so it might be 7.2 in. Build to the actual figure, not the target.
- Letting risers vary across the flight. Steps must be uniform. Even a small difference between the first or last riser and the rest is a trip hazard and usually a code violation. Codes typically allow only about 3/8 in of variation across the whole flight.
- Ignoring the total run and headroom. A comfortable stair can be longer than the opening allows. Check that the total run fits the floor space and that there is enough headroom above the lower steps before you commit to a layout.
Glossary
- Total rise
- The vertical distance from one finished floor to the next, which the stairs must span.
- Riser
- The vertical face of a single step, that is, the height you climb with each step.
- Tread (going)
- The horizontal surface you step on, measured in depth from one step nosing to the next.
- Total run
- The horizontal length the whole flight covers, equal to the number of treads times the tread depth.
- Stringer
- The sloped board, usually notched, that supports the treads and risers along the side of the stairs.
- Nosing
- The front edge of a tread that overhangs the riser below, giving a little extra foot room.
Frequently asked questions
How do I calculate the number of stairs?
Divide the total rise (floor-to-floor height) by your target step height, around 7 inches, then round to the nearest whole number. For a 108 in rise that is 108 / 7 = 15.43, which rounds to 15 steps. The number of steps equals the number of risers.
What is a comfortable riser height?
Around 7 inches (about 18 cm) is widely considered the most comfortable riser for everyday stairs. Building codes commonly cap the riser at 7 3/4 inches, and going much below 6 inches makes a flight feel long and shallow.
How is the tread depth chosen?
This tool uses the comfort rule 2 x riser + tread = about 25 inches, so a 7.2 in riser suggests a 10.6 in tread. The deeper the tread, the gentler the stair feels. Most codes require a minimum tread of 10 inches measured nosing to nosing.
What is the difference between rise and run?
Rise is vertical and run is horizontal. The total rise is the height the stairs climb, and a single riser is the height of one step. The total run is the horizontal length the flight covers, and a single tread is the depth of one step.
Why is there one fewer tread than riser?
The last riser lifts you onto the upper floor, and that floor acts as the final tread, so you never build a separate tread at the very top. A 15-step flight therefore has 15 risers but only 14 treads to cut.
Does this calculator replace a building code check?
No. It gives a sound starting layout using common comfort rules and typical US limits, but riser, tread, headroom and handrail requirements vary by region and by whether the stair is interior, exterior or for a deck. Always confirm with your local code and inspector.
Sources
- R311.7 Stairways (International Residential Code) , International Code Council
- Stair Riser Heights and Tread Depths , U.S. Occupational Safety and Health Administration