Work out your stair
Floor-to-floor rise is the only number that cannot change.
How this calculator works
- Risers = round(rise ÷ 7), minimum two. Seven inches is the comfortable target riser height for a domestic stair.
- Riser height R = rise ÷ risers. Dividing the rise equally is what guarantees identical risers.
- Going G = 25 − 2R, clamped between 9 and 12.5 inches. This is the classic stair formula and it holds across every standard.
- Treads = risers − 1, because the top riser lands on the upper floor and needs no tread.
- Total run = treads × going, compared against the run you have available.
- Cost = risers × construction rate per step, plus balustrade by running foot.
| Floor-to-floor rise | Risers | Riser height | Going | Total run |
|---|---|---|---|---|
| 108 in (9 ft) | 15 | 7.20 in | 10.60 in | 12.4 ft |
| 114 in (9 ft 6 in) | 16 | 7.13 in | 10.75 in | 13.4 ft |
| 120 in (10 ft) | 17 | 7.06 in | 10.88 in | 14.5 ft |
| 126 in (10 ft 6 in) | 18 | 7.00 in | 11.00 in | 15.6 ft |
| 132 in (11 ft) | 19 | 6.95 in | 11.11 in | 16.7 ft |
Total run is what usually decides the shape. A 10 ft floor-to-floor stair needs 14.5 ft of clear length as a straight flight, which almost no Mumbai duplex has — hence the L-shape with a landing, which folds the same geometry into about 9 ft of length plus the landing.
Design and build under one accountable roof
Worked example — a 10 ft floor-to-floor duplex stair
| Step | Arithmetic | Result |
|---|---|---|
| Risers | round(120 ÷ 7) | 17 |
| Riser height | 120 ÷ 17 | 7.06 in |
| Going | 25 − (2 × 7.06) | 10.88 in |
| Treads | 17 − 1 | 16 |
| Total run | 16 × 10.88 | 174 in / 14.5 ft |
| Run available | as entered | 12 ft |
| Verdict | 14.5 > 12 | Needs an L-shape |
| 2R + G check | (2 × 7.06) + 10.88 | 25.0 in — comfortable |
| RCC with stone treads | 17 × ₹9,500 | ₹1.61 L |
The rules that are not negotiable
Headroom is the first. Eighty inches of clear height measured vertically from the nosing of every tread, all the way up. In a duplex where the stair passes under the upper slab or under its own upper flight, this is the constraint that most often fails, and it is discovered when somebody hits their head. Check it at the third-from-top tread, which is where it is usually tightest.
Equal risers is the second. The human gait calibrates to the first two steps of a flight and then stops looking. A riser 15 mm taller than the others, which happens routinely when a floor finish is added after the stair is cast, is exactly the kind of variation that trips people. Set out the stair from finished floor level to finished floor level, not from slab to slab, and confirm the finish thicknesses in writing before casting.
Third, the balustrade. Handrail at 34 to 38 inches above the nosing, and no gap anywhere in the balustrade through which a 100 mm sphere can pass. In a home with small children that second rule is the whole point of the balustrade, and horizontal rails — which look excellent in photographs — are a ladder. Vertical balusters or a glass panel are the safe answers.
Be clear about what is audited here and what is not. Riser, going, the 2R + G comfort check, headroom, handrail height and the 100 mm sphere rule are code and geometry, and they do not move. The per-step and balustrade money is different: a staircase falls outside the residential rate card, which prices flats, so these are Greenbox’s own current Mumbai figures for duplex and villa work at October 2026 rather than rates reconciled against billed projects the way our flooring, joinery and civil numbers are. Treat the output as a planning figure: accurate enough to brief a landlord, a bank or a family, and not accurate enough to sign a contract against.
What this tool does not cover
- Structural design. A cantilevered or floating stair needs an engineer, not a calculator.
- Winders and tapered treads, which follow additional rules on minimum going at the narrow end.
- Municipal and society requirements, which for anything above a private duplex may set minimum widths and maximum riser heights.
- The landing itself, which must be at least as deep as the stair is wide.
- Finishes — stone treads, nosing profiles, anti-slip strips and the soffit below.
- Under-stair storage or a powder room, which is joinery and civil work priced separately in the civil work estimator.
Selected work by Greenbox Design Studio. Tap any image to enlarge.
Frequently asked questions
How do I calculate the number of stairs?+
Divide the floor-to-floor height by 7 inches and round to the nearest whole number. A 120-inch rise gives 17 risers. Then divide the rise by that number to get the exact riser height, so every riser in the flight is identical.
What is the 2R + G rule?+
Twice the riser height plus the going should total 24 to 25 inches. It reflects how a normal stride shortens as it climbs, and a stair that satisfies it feels comfortable at walking pace. A stair that does not will feel either cramped or oddly stretched.
What is the minimum headroom for a staircase?+
Eighty inches of clear height, measured vertically from the nosing of each tread. It is the most commonly violated rule in a domestic duplex and it is usually tightest two or three treads from the top, where the stair passes under the upper slab.
How wide should a staircase be?+
Thirty-six inches is the workable minimum for a private home, 42 is comfortable and 48 is generous. Below 36 inches two people cannot pass and furniture cannot be carried up, which becomes obvious on the day the sofa arrives.
What does a staircase cost to build?+
₹9,500 per step for RCC with stone treads, ₹14,000 for an MS stringer with timber treads, ₹26,000 for full timber and ₹34,000 for cantilevered floating treads. A 17-riser RCC stair is therefore about ₹1.6 lakh before the balustrade, which adds ₹2,800 to ₹4,500 per running foot.