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Stair Calculator
A stair calculator works out the layout of a staircase from three measurements. Enter the total rise — the vertical distance from the lower floor to the upper floor — plus the riser height you are aiming for and the tread depth you want, and it gives you the number of risers, the actual riser height, the number of treads, and the total run. It is the first step in planning a staircase, whether you are building new stairs, replacing old ones, or checking whether a design will fit the space you have. It also handles L-shaped and U-shaped stairs with a landing, and offers one-click presets for common riser and tread combinations.
Measure total rise floor to floor, not floor to ceiling. Risers of about 7–7.75 in and treads of at least 10 in are the usual guidance.
L-shaped turns 90° at the landing; U-shaped turns 180°.
The landing platform, usually at least 36 in square.
| Number of risers | |
| Actual riser height | |
| Number of treads | |
| Total run | |
| Stair type | |
| Flight 1 | |
| Flight 2 | |
| Landing | |
| Path along both flights |
How it works
A staircase is built from two repeating parts. The riser is the vertical face of each step — the height you climb with every step you take. The tread is the horizontal surface you stand on — the depth of each step from its front edge to its back edge.
The calculator starts by dividing the total rise by your target riser height. That division almost never lands on a whole number, and you cannot build half a step, so the answer is rounded to the nearest whole number of risers. That rounded count is the number of steps in your staircase. Then the calculator divides the total rise by that whole number of risers to find the actual riser height — the height every step will really be.
The formulas are:
Actual riser height = Total rise ÷ Risers
Treads = Risers − 1
Total run = Treads × Tread depth
The number of treads is one less than the number of risers because the upper floor itself acts as the final tread. You climb 14 risers to reach a floor 108 inches up, but you only need 13 treads on the way — the fourteenth step is the floor you arrive on. The total run follows from that: 13 treads, each 10 inches deep, cover 130 inches of floor.
When the run is too long for one straight flight, the stairs turn at a landing. An L-shaped stair turns 90 degrees: the first flight climbs about half the risers, you step onto a flat landing, then the second flight climbs the rest in a new direction. A U-shaped stair turns 180 degrees, so the two flights run side by side in opposite directions. The calculator splits the risers as evenly as it can between the two flights — for 14 risers that is 7 and 7 — and each flight's run is its own treads times the tread depth, plus the landing in between. The landing is usually at least 36 inches square, so there is room to turn comfortably.
Comfort and safety pull in opposite directions here. Shorter risers and deeper treads feel easier and safer to climb, especially for children, older people, and anyone carrying something, but they need more steps and more floor space. Taller risers and shallower treads save space but feel steeper and tire legs faster.
Before you cut any timber, measure twice. Measure the total rise at several points along the planned staircase, because floors are rarely perfectly level, and use the largest measurement so no step ends up taller than planned.
Worked example
Daniel is building stairs between two floors with a total rise of 108 inches — 9 feet from the lower floor surface to the upper floor surface. He wants a riser height of about 7.5 inches and a tread depth of 10 inches, and he wants to know how many steps he needs and how much floor space the stairs will take.
First, the riser count: 108 ÷ 7.5 = 14.4, which rounds to 14 risers. Next, the actual riser height: 108 ÷ 14 = 7.714 inches, or about 7.71 inches per step — a little taller than the 7.5-inch target, but even across all 14 steps and within the usual guidance. The tread count is 14 − 1 = 13 treads, because the upper floor is the final step. Finally, the total run is 13 × 10 = 130 inches, or just under 11 feet of floor space.
Daniel can now check the plan against his room: the stairs need 130 inches of run, every step is 7.71 inches high, and the layout is even and comfortable. If 130 inches is more run than his room allows, he knows the trade-off — a taller riser would shorten the run but make the stairs steeper — and he can test a new target in the calculator before he changes the design.
FAQ
What is the difference between a riser and a tread?
The riser is the vertical face of a step — the height you climb with each step. The tread is the horizontal part you stand on — the depth of each step from front to back.
How many risers do I need for my stairs?
Divide the total rise — the vertical distance from the lower floor to the upper floor — by the riser height you want, then round to the nearest whole number. For example, a total rise of 108 inches divided by a target riser of 7.5 inches is 14.4, which rounds to 14 risers.
What is a comfortable riser height?
Most people find risers between 7 and 7.75 inches comfortable, and many building codes set about 7.75 inches as the maximum riser height, with treads at least 10 inches deep. Shorter risers feel easier to climb but need more steps and more floor space; taller risers save space but feel steeper.
Why is the number of treads one less than the number of risers?
Because the top step is the upper floor itself. If a staircase has 14 risers, you climb 14 vertical steps, but you only need 13 treads — the upper floor acts as the final tread.
What is an L-shaped stair?
An L-shaped stair has two flights joined by a flat landing, with the second flight turning 90 degrees from the first. It fits a corner and breaks a long climb into two shorter flights.
Should I trust this calculator for building stairs?
Use it for planning and estimating, then check the result against the building code where you live and confirm the measurements on site before you cut anything. Codes set limits on riser height, tread depth, headroom, and handrails, and a local builder or inspector can confirm what applies to your project.