This calculator develops the geometry of one straight stair flight between two finished floor levels. It calculates or checks a whole number of risers, tread run or going, total run, pitch, stringer length and optional headroom.
Start with the finished floor-to-floor height
Measure from the top of the finished lower floor to the top of the finished upper floor. A structural slab measured before screed, flooring, decking or other finishes are installed can produce an incorrect first or last riser when the project is completed.
Stair terms used across English-speaking markets
| Calculator term | Other wording you may see | Meaning |
|---|---|---|
| Rise per step | Riser height | Vertical nosing-to-nosing distance between adjacent steps |
| Tread run / going | Run in Canada, going in the UK and Australia, tread depth in some US guidance | Horizontal nosing-to-nosing distance used in the stair geometry |
| Total horizontal run | Stair run or footprint length | Combined horizontal distance covered by all treads |
| Stringer pitch-line length | Sloping stringer length | Diagonal geometric length before end details and structural checks |
Automatic mode selects a whole number of risers
The preferred riser height is a target rather than the final answer. The calculator compares whole riser counts and selects the closest practical option while considering the maximum rise, minimum tread run and maximum pitch entered in Advanced settings.
What happens when the preferred rise is 7 in?
Answer: A 108 in height divided by 7 in is about 15.43. The calculator must choose a whole number, then divide the full 108 in by that count to give equal risers.
Explanation: The selected count is checked against the entered maximum riser, tread and pitch limits. The preferred value is not rounded independently for every step.
Fixed-count mode checks an existing proposal
Use a fixed count when a drawing, existing opening or framing layout already sets the number of rises. The calculator keeps that number and reports the resulting rise, run, angle and any conflict with the limits you entered.
Enter either one tread run or the total space available
Two ways to define the horizontal geometry
| Known dimension | Enter | Calculator returns |
|---|---|---|
| Run or going for each tread | The horizontal nosing-to-nosing distance | Total stair run, pitch and stringer length |
| Space available in the room | The complete horizontal run | The run of each tread and whether the entered limits can be met |
A conventional floor-to-floor flight normally has one fewer separate treads than risers because the finished upper floor or landing acts as the final walking surface.
Stair angle comes from total rise and total run
The pitch is calculated from a right triangle: finished floor-to-floor height is the vertical side and total horizontal run is the horizontal side. Changing the riser count alone does not change the overall angle when those two full dimensions remain unchanged.
The 2R + G result is a proportion check, not a universal approval
Twice the rise plus the going is shown as an additional planning measure. A broad 550–700 mm band appears in UK and Australian stair guidance, but it does not replace separate limits on rise, going, pitch, flight length or the requirements applying to a particular stair type.
Stringer pitch length is not the final cut length
The pitch-line length is the hypotenuse formed by total rise and total run. Real stringers normally need additional stock for the top connection, bottom bearing, cuts and trimming, so the calculator provides a separate editable end allowance.
The length result does not select stringer size, remaining throat depth after notching, number of stringers, allowable span, material grade or load capacity. Those are structural decisions.
The optional headroom estimate uses simplified straight-flight geometry
Enter the horizontal floor-opening length measured back from the upper landing and the vertical depth to the underside of the floor structure. The result estimates the vertical clearance above the nosing line at the opening edge.
Confirm headroom on the drawing and on site across the full stair width. Beams, ceiling finishes, landings, turns and the top connection can reduce the actual clearance.
Planning limits are editable because local rules are not universal
Residential stair terminology and dimensional rules differ across the United States, Canada, the United Kingdom and Australia, and local or state, provincial and territorial adoption can modify a national model or guidance document. The calculator therefore compares the geometry with values you enter instead of claiming universal code compliance.
How to use the regional wording
| Region | Common wording | Practical calculator setting |
|---|---|---|
| United States | Riser height and tread depth or run | Imperial is the default; enter the limits adopted for the project location |
| Canada | Rise, run and tread depth | Metric code values are common; verify the province or territory |
| United Kingdom | Rise, going and pitch | Metric mode uses the same geometry and displays 2R + G |
| Australia | Riser, going and slope relationship | Metric mode supports the entered rise, going, angle and headroom limits |
Checks still required before stairs are built
- Recheck both finished floor levels and the installed tread thickness.
- Keep every rise and tread run uniform within the flight.
- Verify stair width, landings, doors and door swings.
- Check headroom along the complete walking line and across the stair width.
- Specify handrails, guards or balustrades, open risers and fall protection.
- Design stringers, connections and supports for the material, span and loads.
- Confirm the current requirements adopted by the local authority before cutting or ordering components.
Frequently asked questions
Why is the tread count one less than the riser count?
The first rise reaches the first tread and the final rise reaches the upper floor or landing. A conventional straight flight with 16 rises therefore has 15 separate treads between the two floors.
Can this be used for L-shaped or U-shaped stairs?
Each straight flight can be calculated separately, but the distribution of risers, landing dimensions, winders and headroom around the turn require a complete stair layout.
Does the calculator prove that the stairs meet code?
No. It checks straight-flight geometry against limits entered by the user. The applicable code or building-control authority must also be consulted for landings, width, headroom measurement, handrails, guards, flight length, special stairs and structural design.