Stair Calculator – Rise, Run, Steps & Stringer Length

Calculate how many stair steps you need from floor-to-floor height, then find actual riser height, tread run, total run, stair angle, stringer length and the 2R + G step-rule value.

Stair rise, run and step dimensions

m
cm
cm
m

Optional local-limit check

Enter values from the building rules or project standard that applies to you. Leave 0 to disable a check.

cm
cm

Stair calculation result

Number of risers
—
Actual riser height—
Number of treads—
Tread going / run—
Total horizontal run—
Stair angle—
Stringer / flight length—
2R + G step rule—
Tread surface area—
Local-limit check—
—

Geometry only. Always verify finished dimensions, headroom, landings, width, nosings, handrails, guards and structural details against the requirements for your project.

Your calculation

What does your stair geometry mean?

The live interpretation updates with the rise, riser count and available run.

Risers—
Actual riser—
Total run—
Check the geometry against your project requirements.

Does the result look realistic?

What affects the result most?

What to do with the result

Next step

Continue your construction estimate

Use the stair geometry to continue with the structure, finish or adjoining outdoor platform.

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How to calculate stair rise and run

A straight stair starts with one measurement that cannot be guessed: the total rise from finished lower floor to finished upper floor. Divide that height into equal risers. In automatic mode, the calculator compares the total rise with your target riser height, rounds to a whole number of risers and then recalculates the exact equal riser height.

If the upper floor or landing is the final walking surface, a flight with n risers normally has n − 1 separate treads. The horizontal run is then the tread going multiplied by the number of treads. Select the alternate top-tread option only when your geometry genuinely includes an additional tread at the top.

Where to get the stair input data

Finished floor-to-floor rise

Measure vertically from the finished walking surface at the lower level to the finished walking surface at the upper level. Include known floor build-ups, finishes and thresholds. A structural slab-to-slab dimension can be wrong for the finished stair if the floor finishes change the final levels.

Available run and local limits

Take the clear horizontal run from the stair layout or measured opening. Get maximum riser, minimum going and any other required dimensions from the rules, approved drawings or specification that actually applies to the building. Do not copy a limit from an unrelated country or building type.

Measure twice: stair geometry is sensitive to small changes in finished height because the number of equal risers must be a whole number.

Stair rise and run formulas

Actual riser = total rise ÷ number of risers. When you enter a tread going, total run = treads × going. When you enter the available run instead, going = available run ÷ treads.

These simple relationships are the core of a stair rise and run calculator. Equal dimensions matter: the finished stair should not be built from mixed riser heights produced by rounding each step separately.

Stair stringer length and angle

The calculator treats the straight flight as a right triangle. The horizontal leg is total run and the vertical leg is total rise. The sloping flight or theoretical stringer line is √(rise² + run²), while the stair angle is atan(rise ÷ run).

This is a geometry length, not a structural cut list. Real stringers need extra stock for end cuts, bearing and project-specific detailing.

2R + G stair formula: checking step proportions

A common stair-planning relationship compares two riser heights with one tread going: 2R + G. In German-speaking stair design this is widely known as the Schrittmaßregel. A value around a normal human step length is often used as a comfort check, but the formula is not a building-code approval.

The result panel shows the current 2R + G value automatically. If a stair has a relatively high riser and short going, the value and angle help reveal how steep the geometry is. If you have a fixed floor height but more horizontal space, increasing the going lowers the angle without changing the number of risers.

Fit a staircase into an available horizontal run

Choose Fit to available total run when the stairwell or room gives you a fixed horizontal space. The calculator first determines the riser count, then divides the available run by the number of treads. This answers a common planning question: “If my floor height is fixed, what tread depth can I get in the space I have?”

If the resulting tread is too short for the rule that applies to your project, the geometry needs to change. Possible design changes include more horizontal space, a landing and second flight, a different stair arrangement or another professionally designed solution. Do not force a straight stair into an opening by making irregular steps.

One-riser sensitivity: what changes if you add or remove one riser?

This is the stair-specific comparison that is easy to miss in a basic calculator. For the same floor height, changing the riser count by just one changes the actual riser height. If tread going is fixed, it also changes the number of treads, total horizontal run and stair angle. If the available run is fixed, the same space is divided across a different number of treads, so the going changes instead.

The table updates from your current inputs.

OptionRisersActual riserTreadsGoingTotal runAngle2R + G

This comparison is geometry only. It helps you see sensitivity before you verify the chosen option against project-specific limits, headroom, landings, structure and other requirements.

Example stair rise and run table

The table below is an educational comparison using a 17.5 cm target riser, a 28 cm going and an upper landing as the final step. It is not a code table; it simply shows how whole-riser rounding changes the actual rise.

Total riseRisersActual riserTreadsTotal run
2.40 m1417.14 cm133.64 m
2.60 m1517.33 cm143.92 m
2.80 m1617.50 cm154.20 m
3.00 m1717.65 cm164.48 m

For students and apprentices: stair calculation practice

Use these tasks to practise stair rise and run, number of steps, stair angle, Pythagoras and the 2R + G formula. Load the values, calculate the answer yourself and then reveal the worked solution. The answers use the same calculation engine as the live stair calculator.

Exercise 1: 2.80 m floor height

A straight stair rises 2.80 m. Use a target riser of 17.5 cm and a going of 28 cm. The upper floor is the final step.

Exercise 2: fit into 3.60 m

A floor height of 2.70 m must fit into 3.60 m of horizontal run. Use a 17 cm target riser and calculate the resulting going.

Exercise 3: US deck stair

A deck is 96 in above grade. Use a 7 in target riser and 10.5 in going. Calculate risers, treads, run, angle and stringer line.

Why this calculator does not preload a universal “code-compliant” stair

This calculator is a geometry and material-planning aid, not structural design or regulatory approval. Stair requirements can govern riser height, tread going, width, landings, headroom, nosings, handrails, guards, consistency and many other details. Different regulatory systems and different building uses can apply different dimensional rules, so a single global preset would be misleading.

The optional maximum-riser and minimum-going fields therefore stay under your control: enter values from the rules or approved project documents that actually apply to your stair. A pass in these two custom checks still does not verify the other requirements.

Measure finished-floor levels, not unfinished structural levels, and verify the final design against the rules, drawings and product details that apply to the project. For structural stairs, altered openings or uncertain conditions, use a qualified designer or building professional.

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FAQ – stair rise, run, steps, angle and stringer length

How do I calculate how many steps I need for a staircase?
Measure the total vertical rise from finished floor to finished floor, divide it by a target riser height, round to a practical whole number of risers, then divide the total rise by that number to get the actual riser height.
What is the difference between a riser and a tread?
A riser is the vertical rise from one step level to the next. A tread or going is the horizontal step distance. In a typical floor-to-floor flight where the upper floor acts as the final landing, the number of treads is one less than the number of risers.
How do I calculate stair rise and run?
Actual riser height equals total rise divided by the number of risers. Total run equals the number of treads multiplied by the tread going, unless you choose the fit-to-run mode, where the calculator derives the tread going from the available horizontal run.
Can I use this as a stair stringer calculator?
The calculator estimates the straight sloping flight or stringer length from total rise and total run using the Pythagorean theorem. Real stringer stock length, cuts, bearing, thickness and structural design still need to be checked separately.
What is the stair angle?
The stair angle is the angle of the flight above horizontal. It is calculated from total rise and total run. A shorter run for the same floor height produces a steeper angle.
What is the 2R + G stair formula?
The step-rule value is twice the riser height plus the tread going. It is a traditional comfort-planning relationship often used to compare stair proportions. It is not a substitute for local building regulations.
Can the calculator fit stairs into an available horizontal space?
Yes. Choose Fit to available total run. After determining the number of risers and treads, the calculator divides the available run by the number of treads to calculate the resulting tread going.
Why are there fewer treads than risers?
When the upper floor or landing is the final walking surface, the last rise ends on that floor and does not need a separate tread. In that common layout, treads equal risers minus one. You can switch to include a top tread if your geometry requires it.
Does the calculator check building code?
No. Stair rules vary by country, building type, use and jurisdiction. The optional limit fields let you compare the result with maximum-riser and minimum-going values that you enter from the rules applicable to your project.
Can I calculate stair dimensions in feet and inches?
Yes. Select US customary units. The calculator converts the geometry internally and displays rise, going, total run and stringer length in inches and feet where useful.
Can I estimate tread surface area?
Yes. Enter the stair width. The calculator multiplies the tread going by the stair width and number of treads to estimate the horizontal tread surface area, useful for a first material takeoff.
What happens if I add or remove one riser?
Changing the riser count changes the actual riser height. With a fixed tread going it also changes the number of treads, total run and stair angle; with a fixed available run it changes the going because the same run is shared across a different number of treads. The live one-riser comparison shows all three cases.
Does this calculator check stair headroom, landings or handrails?
No. It calculates straight-flight geometry only. Headroom, landings, width, nosings, handrails, guards, structural support and other project requirements must be checked separately against the rules and drawings that apply to the building.
Can students and apprentices use this stair calculator?
Yes. The learning section includes metric and US practice problems for number of risers, actual rise, tread going, total run, stair angle, stringer length and the 2R + G step rule.