🪜 Stair Calculator
Find the number of risers, the exact riser height, tread depth, total run, stair angle, and stringer length — from one measurement, the total rise. Interior, deck, and utility stairs. Free, no sign-up.
A stair calculator sizes a staircase from its total rise — the floor-to-floor height. It works out how many risers the flight needs, the exact height of each one, the total run on the floor, the stair angle, and the length of the stringer board that carries the steps. The core formulas are:
How to size a staircase in 3 steps:
- Measure the total rise from finished floor to finished floor, in inches.
- Set the tread depth and target riser height — 10″ tread and 7.5″ riser are standard.
- Click Calculate Stairs to see riser count, riser height, treads, run, angle, and stringer length.
For example, a 108-inch total rise with a 7.5″ target gives 14 risers at 7.71 inches each. With 13 treads at 10 inches, the run is 10.8 feet and the stringer measures about 14.1 feet.
Stair Calculator
Enter your total rise — get riser count, riser height, run, angle and stringer length.
Size a Staircase From One Number –
the Total Rise Floor to Floor
A whole staircase follows from a single measurement. Get the total rise right and the riser count, riser height, run, angle, and stringer length all fall out of it. This free calculator does that math — and checks the result against the comfort and code ranges before you cut a board.
⚡ Try the Calculator NowA Staircase Is One Measurement, Worked Out Carefully
Stairs look complicated, and a badly built one is genuinely dangerous. But the design comes down to a single number you can take with a tape measure: the total rise, floor to finished floor. Everything else — how many steps, how tall each one, how far the flight reaches across the room — is arithmetic that follows from it.
Here is the part people get wrong. You cannot just divide the rise by seven and start cutting. The riser count has to be a whole number, every riser in the flight has to match, and the result has to land inside the code limits for height and depth. Miss any of those and you get an uneven step at the top or bottom — the exact spot where people trip.
This Stair Calculator handles all of it. Enter the total rise, set the tread depth and a target riser, and it returns the riser count, the exact riser height, the tread count, the total run, the stair angle, and the stringer length — then checks the layout against the comfort rule builders use.
How the Stair Calculator Works
One required measurement, two design choices, one click. Here is what each field does and why it matters.
Pick the Stair Type
Interior, deck, or utility. The tab sets sensible starting defaults — interior stairs favor a 7.5″ riser, deck stairs a lower riser and deeper tread, utility stairs a steeper riser to save space.
Enter the Total Rise
This is the one measurement that matters most: the vertical distance from the lower finished floor to the upper finished floor, in inches. A typical home floor-to-floor is around 105 to 114 inches.
📏 Measure to the finished floor, not the subfloor.Set the Tread Depth
How deep each step is, front to back. Codes generally want at least 10 inches. Interior stairs sit near 10–11″; outdoor stairs are often deeper for a surer footing.
📐 A deeper tread is more comfortable but uses more floor space.Set a Target Riser Height
The riser height you are aiming for — usually 7 to 7.5 inches. The calculator divides the rise by this target, rounds to a whole number of risers, then works back to the exact height each one will be.
Add Width, Stringers & Waste
Stair width sets the footprint. In Advanced mode, the stringer count and a waste factor turn the stringer length into a total figure for ordering lumber.
Hit Calculate — Read Every Number
Instantly see the riser count, exact riser height, tread count, total run, stair angle, stringer length, and the 2R + T comfort check.
✅ Risers = round(Total Rise ÷ Target Riser)The Stair Formulas, Explained
A staircase is a right triangle with steps drawn inside it. Four short formulas turn the total rise into a full layout.
The riser count. Divide the total rise by your target riser height, then round to the nearest whole number. You cannot have a fractional step, so this rounding is the heart of the whole calculation. A 108-inch rise with a 7.5-inch target gives 108 ÷ 7.5 = 14.4, which rounds to 14 risers.
The exact riser height. Now reverse it. Divide the total rise by that whole riser count to get the real height of each step. With 14 risers carrying 108 inches, every riser is 108 ÷ 14 = 7.714 inches. That is the number you actually mark out — and every riser in the flight gets it, with none left over.
The treads and the run. A flight always has one fewer tread than it has risers, because the top riser delivers you onto the finished floor. Fourteen risers means thirteen treads. Multiply the tread count by the tread depth and you have the total run — the horizontal floor space the staircase eats up. Thirteen treads at 10 inches is a 130-inch run, just under 11 feet.
The stringer. The stringer is the diagonal board that carries the steps, and it is the hypotenuse of the rise-run triangle. Square the total rise, square the total run, add the two, and take the square root. A 108-inch rise and a 130-inch run give a stringer of about 169 inches — just over 14 feet of board per stringer.
Riser, Tread & Code Tables
A handful of numbers covers almost every staircase. The riser and tread limits are the ones worth knowing before you start.
| Dimension | Typical Range | Common Code Limit |
|---|---|---|
| Riser height | 7″–7.5″ | 7.75″ maximum |
| Tread depth | 10″–11″ | 10″ minimum |
| Stair width | 36″+ | 36″ minimum |
| Headroom | 80″+ | 80″ minimum |
The core formula in plain words: divide the total rise by your target riser, round to a whole number for the riser count, then divide the rise by that count for the exact riser height. A 108-inch rise gives 14 risers at 7.71 inches each.
Risers for a Typical Floor-to-Floor Rise
| Total Rise | Risers (7.5″ target) | Exact Riser Height |
|---|---|---|
| 96″ (8 ft) | 13 | 7.38″ |
| 105″ | 14 | 7.50″ |
| 108″ (9 ft) | 14 | 7.71″ |
| 114″ | 15 | 7.60″ |
| 120″ (10 ft) | 16 | 7.50″ |
How Steep the Common Layouts Feel
| Riser / Tread | Stair Angle | Character |
|---|---|---|
| 6″ riser / 12″ tread | ~27° | Gentle — easy public stairs |
| 7″ riser / 11″ tread | ~32° | Comfortable residential |
| 7.5″ riser / 10″ tread | ~37° | Standard house stairs |
| 7.75″ riser / 9″ tread | ~41° | Steep — utility and basement |
Most home staircases land between 32 and 40 degrees. Steeper than that starts to feel like a ladder; much shallower eats floor space a house rarely has to spare.
Factors That Shape a Staircase
The formulas give a clean layout, but a staircase has to live inside a real building. These are the factors that push the design one way or another.
Interior, Deck & Utility Stairs Compared
The three stair types in this calculator are not different math — they are different starting points, tuned to where the stairs will live.
| Type | Best For | Riser / Tread | Trade-off |
|---|---|---|---|
| Interior | Main house staircases | ~7.5″ / ~10″ | Balances comfort against floor space |
| Deck / Exterior | Decks, porches, outdoor steps | ~7″ / ~11″ | Safer footing, but needs more run |
| Utility / Steep | Basements, attics, garages | ~7.75″ / ~9.5″ | Saves space, but steeper to climb |
How to Lay Out a Staircase: A Phase-by-Phase Roadmap
A clean staircase is mostly careful layout before any wood is cut. Here are the four phases from an empty opening to a marked stringer.
Measure straight down from the upper finished floor to the lower finished floor. Account for any flooring not yet installed at either level. This number drives everything, so take it twice and make sure the two readings agree.
Pick a target riser height and a tread depth, then calculate. Check the riser height against code, and confirm the 2R + T figure lands in the comfortable 24–25 inch band before going further.
Take the total run from the calculator and check it fits the floor where the stairs will land. Then confirm there is clear headroom above every step. If either falls short, adjust the tread depth or riser count and recalculate.
Using a framing square set to the riser height and tread depth, step the layout down the stringer board. Mark every notch, double-check the count, and cut. The first stringer becomes the template for the rest.
What a Staircase Costs to Build
A staircase ranges from a weekend's lumber bill to a major finish-carpentry job. The split between materials and labor depends almost entirely on the finish.
A basic set of stairs is not expensive in materials. Pressure-treated stringers, treads, and fasteners for a short deck stair often come in under $200. The cost climbs with the finish: hardwood treads, finished risers, a railing system, balusters, and trim turn a structural staircase into a piece of joinery, and the labor follows the same curve.
Use the stringer length and count from the calculator to size the lumber. A flight needs a stringer at each side and usually one or more down the middle, each cut from a board long enough for the full diagonal — so the total stringer lumber is the stringer length multiplied by the stringer count, plus a waste margin.
Example Stair Calculations
Three staircases, three settings — each worked through with verified math so you can sanity-check your own. All assume a 10% lumber waste factor.
Building a Safe, Comfortable Staircase
A staircase is one of the few things in a house people use without looking. That is exactly why the details below matter — the body trusts every step to be the same.
The single rule that prevents the most falls is equal risers. People climb on autopilot, their feet expecting each step to match the one before. A riser that is even half an inch off — almost always the first or last one — breaks that rhythm at the worst possible moment. This is the whole reason riser height is calculated rather than eyeballed.
The second habit is checking the layout against the space before cutting anything. A staircase that works on paper can still fail to fit: the run lands in a doorway, or the headroom pinches under a floor opening. The numbers come first, but the tape measure in the actual stairwell has the final word.
Six Habits for a Sound Staircase
When This Calculator Is the Wrong Tool
The arithmetic here is exact, but a staircase is a structural element with details a calculator cannot judge. Here is where the output needs a builder's eye.
1. It assumes a straight flight. The calculator models a single straight run of stairs. Winders, L-shaped and U-shaped stairs with landings, and spiral stairs all change the geometry — each straight segment can be figured separately, but the turns themselves are a different problem.
2. It does not check headroom or fit. The calculator returns the total run, but it cannot see your building. Whether that run lands clear of doorways and walls, and whether there is 80 inches of headroom above every step, is something only a measurement of the actual space can answer.
3. The stringer figure is the diagonal length. It tells you how long a board each stringer needs to be. It does not account for the framing-square layout of the notches, the strength of wood left after cutting, or how the stringer attaches at top and bottom — all of which belong to the build.
4. Codes vary and change. The riser, tread, width, and headroom figures used here reflect common requirements, but building codes differ by jurisdiction and are revised over time. The calculator is a planning tool — the code that governs your project is the authority.
Where to go instead: For the lumber to build treads, risers, and stringers, a board foot calculator sizes the wood. For the slope of a roof above an exterior stair, a roof pitch calculator handles that geometry. This tool's job is the stair layout itself — risers, treads, run, and stringer.
Stair Terms You'll See On This Page
Quick reference for the staircase terms used throughout this calculator.
- Total Rise
- The full vertical height a staircase climbs, measured from the lower finished floor to the upper finished floor.
- Riser
- The vertical face of a single step. Riser height is the total rise divided by the number of risers.
- Tread
- The horizontal surface of a step — the part you stand on. Tread depth is measured front to back.
- Total Run
- The full horizontal distance a staircase covers — the number of treads multiplied by the tread depth.
- Stringer
- The diagonal board, usually notched, that supports the treads and risers along the side of a staircase.
- Nosing
- The small lip where a tread overhangs the riser below it, giving the foot a little extra depth.
- Stair Angle
- The slope of the flight, measured from horizontal. Most residential stairs fall between about 32 and 40 degrees.
- 2R + T Rule
- A comfort check: twice the riser height plus the tread depth should land between roughly 24 and 25 inches.
- Headroom
- The clear vertical space above the stairs. Codes generally require at least 80 inches, measured above every step.
- Flight
- An uninterrupted run of stairs between two floors or between two landings.
- Landing
- A flat platform that breaks a staircase, used to change direction or to divide a long flight.
- Winder
- A wedge-shaped tread used to turn a staircase without a full landing.
- Finished Floor
- The final floor surface, including tile, hardwood, or carpet — the level a staircase must actually meet.
- Framing Square
- An L-shaped tool used to mark the riser and tread notches repeatedly down a stringer board.
Frequently Asked Questions
The most common questions about sizing and building a staircase.
How do I calculate the number of stairs I need?
Divide the total rise — the floor-to-floor height — by your target riser height, then round to the nearest whole number. That gives the number of risers. For a 108-inch rise and a 7.5-inch target, 108 ÷ 7.5 = 14.4, which rounds to 14 risers. The number of treads is always one less than the number of risers.
What is the ideal riser height for stairs?
Most building codes cap the riser height at about 7.75 inches, and a comfortable range is 7 to 7.5 inches. The calculator finds the exact riser height by dividing the total rise by the riser count, so every step is identical — even risers matter more for safety than hitting a round number.
What is the difference between a rise and a run?
The rise is the vertical part of a step, and the run is the horizontal part. Total rise is the full floor-to-floor height, and total run is the full horizontal distance the staircase covers. A single step has one riser height and one tread depth; the staircase has a total rise and a total run.
How deep should a stair tread be?
Building codes generally require a tread depth of at least 10 inches, measured from the face of one riser to the next. Interior stairs are often built right at 10 to 11 inches, while exterior and deck stairs are frequently deeper, around 11 to 12 inches, because a deeper tread is easier and safer to use outdoors.
How do I calculate stringer length?
The stringer is the diagonal board that carries the steps, and its length is the hypotenuse of the rise-run triangle. Square the total rise, square the total run, add them, and take the square root. For a 108-inch rise and a 130-inch run, the stringer is about 169 inches, or just over 14 feet.
What is the 2R plus T rule for stairs?
The 2R + T rule is a comfort check: twice the riser height plus the tread depth should land between about 24 and 25 inches. It reflects the natural length of a human stride on stairs. A staircase whose 2R + T falls in that range feels even and comfortable; one far outside it feels cramped or stretched.
How many treads does a staircase have?
A staircase always has one fewer tread than it has risers. The top riser brings you up to the level of the finished upper floor, so that final step does not need a separate tread. A flight with 14 risers has 13 treads.
What is the maximum stair angle?
Comfortable staircases sit between about 30 and 37 degrees. Building codes effectively cap a standard stair around 42 to 45 degrees through the riser and tread limits. Anything steeper is treated as a ship's ladder or alternating-tread device and has its own separate rules.
How many stringers does a staircase need?
A staircase needs a stringer at each side and usually one or more in the middle. Stairs up to about 36 inches wide typically use three stringers; wider stairs need a stringer roughly every 16 inches of width to keep the treads from flexing underfoot.
Do all the steps in a staircase have to be the same height?
Yes. Building codes require the risers in a single flight to be nearly identical — usually within about three-eighths of an inch of each other. Uneven risers are a serious trip hazard, because people climb stairs by feel and expect every step to be the same. This is why the riser height is calculated, not guessed.
What total rise should I measure for stairs?
Measure the total rise from the surface of the lower finished floor to the surface of the upper finished floor. Include any flooring that will be added later, since the stairs must meet the final floor levels. Measuring to a subfloor and forgetting the finish thickness throws off every riser in the flight.
How much horizontal space does a staircase take up?
The horizontal space is the total run — the number of treads multiplied by the tread depth. A 14-riser staircase has 13 treads; at 10 inches each, that is 130 inches, or about 10.8 feet of floor space. Steeper stairs with shorter treads take up less run but are harder to climb.
More Tools You'll Love
A staircase is one part of a build. These companion calculators handle the measurements around it.
Size Your Staircase
in 30 Seconds
Enter the total rise — get the riser count, exact riser height, tread count, total run, stair angle, and stringer length. All free.
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