Stair Calculator
This stair calculator lays out a whole flight from one measurement: the total rise. Enter the floor-to-floor height and your tread depth, and you'll get the number of steps, the exact riser height, the total run, the stringer length, and the slope angle. It aims each riser at a comfortable size and keeps them equal, so the stairs feel right and you'll pass a code check. It's free and runs in your browser, you won't need an account, and there's no wait, since the numbers update as you type.
- Number of steps
- Riser height
- Total run
- Stringer length
- Slope angle
Last updated June 17, 2026 Inches, equal risers Reviewed by the Calcowa team
Enter a total rise and a target riser above zero.
All measurements are in inches. Risers stay equal, and a flight has one more riser than tread. Always confirm against your local building code.
How do you calculate stairs?
Stairs start from the total rise, the height from one finished floor to the next. You divide that rise by a comfortable step height, around 7.5 inches, and round to a whole number, since every riser has to be equal. Dividing the total rise by that count gives the exact riser height. The treads are always one fewer than the risers, so multiply the treads by your tread depth to get the total run. The stringer, the angled board that holds the steps, is the diagonal of that rise-and-run triangle, found with the Pythagorean theorem. You don't have to work any of it by hand, since this tool runs it all at once, and it'll flag the result if the riser or tread drifts outside common comfort limits. That's the part folks miss when they eyeball a flight, and it's what keeps the stairs safe.
Laying out a flight, step by step
Here's the quick routine before you cut a stringer:
- 1
Measure the total riseMeasure floor to finished floor, not floor to joist.
- 2
Set your tread depthPick the tread you'll use, often 10 or 11 inches.
- 3
Check the riserThe tool keeps risers equal, so they're safe to climb.
- 4
Cut from the numbersYou'll have risers, treads, run, and stringer length.
Common stair layouts
These use a 10-inch tread and a target riser near 7.5 inches, the same defaults as the tool.
| Total rise | Risers | Riser height | Total run |
|---|---|---|---|
| 36 in (deck) | 5 | 7.20 in | 40 in |
| 96 in (8 ft) | 13 | 7.38 in | 120 in |
| 108 in (9 ft) | 14 | 7.71 in | 130 in |
| 120 in (10 ft) | 16 | 7.50 in | 150 in |
Frequently asked questions
You give it the total rise, which is the floor-to-floor height your stairs need to climb, plus the tread depth you'd like. It divides the rise into equal steps near a comfortable 7.5 inches each, then works out the exact riser height, the number of treads, the total run, and the stringer length. You'll see the slope angle too, so you know how steep the flight turns out before you cut a thing.
Rise is how far each step lifts you vertically, and run is how far each step takes you horizontally, the tread depth you step on. Total rise is all the risers added up, the full height of the staircase, and total run is all the treads added up, the floor space the flight uses. The calculator keeps every riser equal, since uneven risers are the top trip hazard on a staircase.
Most building codes cap the riser near 7.75 inches and ask for a tread of at least 10 inches, and a riser around 7 to 7.5 inches with an 11-inch tread feels easy underfoot. A common rule of thumb is that twice the riser plus the tread lands between 24 and 25 inches. This tool aims for that comfort zone, but it's wise to check your local code before you build, since they're not all identical.
The stringer is the diagonal board that carries the steps, and its length is the hypotenuse of the rise and run triangle. The calculator squares the total rise, squares the total run, adds them, and takes the square root, so you get the straight-line length of the cut board. Add a little for the top and bottom connections, since the figure here is the bare diagonal of the staircase.
It does, and the difference trips people up. A flight always has one more riser than tread, because the top riser lands at the upper floor and needs no tread there. So if the calculator finds 14 risers, you'll cut 13 treads. It shows both numbers clearly, along with the run that those treads add up to, so your material list comes out right.
Yes, it's completely free, with no sign-up, and it runs right in your browser, so nothing you type leaves your device. Bookmark it for the next deck, basement, or porch project, and you'll have your risers, treads, run, and stringer in a second. It's a quick planning tool, so treat the numbers as a starting point and confirm them against your local building code.
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