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Stair Calculator — Risers, Treads, Run, Angle & Stringer

Plan a straight staircase from the floor-to-floor height: the number of risers and treads, the exact riser height, the total run (going), the angle and the stringer length, with a step-by-step marking table. Checks the design against the NBC 2016 residential limits, the US IRC or your own limits, and against Blondel's comfort rule.

Your inputs

Quick start — try a typical case

Measurements In

Check Against

Total Rise (floor to floor)

Finished floor below to finished floor above, including the slab.

Preferred Riser Height

150–175 mm (6–7 in) feels comfortable for most people.

Tread (Going)

Horizontal depth of each step, nosing to nosing.

Your result Live

Steps

18 risers of 167 mm

17 treads of 270 mm — the upper floor is the last step

Riser Height: 167 mm (6.56 in)
Total Run (Going): 4,590 mm (180.71 in)
Angle: 31.7°
Stringer Length (approx.): 5,483 mm (215.88 in)
Comfort (2 risers + 1 tread): 603 mm — within Blondel's comfortable 600–650 mm
Code Check: Meets NBC 2016 residential riser and tread limits
Floor Space of the Flight: 4.86 m² (52.3 sq ft) including the landing step

Marking out — top of each step

18 rows

Step	Height above lower floor	Distance from the first riser
1	167 mm	0 mm
2	333 mm	270 mm
3	500 mm	540 mm
4	667 mm	810 mm
5	833 mm	1,080 mm
6	1,000 mm	1,350 mm
7	1,167 mm	1,620 mm
8	1,333 mm	1,890 mm
9	1,500 mm	2,160 mm
10	1,667 mm	2,430 mm
11	1,833 mm	2,700 mm
12	2,000 mm	2,970 mm

NBC 2016: riser up to 190 mm and tread at least 250 mm for residential buildings (150 mm / 300 mm for most other buildings).

More than about 12 risers in one flight is commonly broken by a landing — check your local building bye-laws.

Keep every riser in a flight the same height — uneven steps are a common cause of falls.

How this is calculated

Risers n = ⌈total rise ÷ maximum riser⌉ (or nearest to your preferred riser) · Riser = rise ÷ n · Treads = n − 1 · Run = treads × tread · Angle = atan(riser ÷ tread) · Comfort = 2 × riser + tread

Riser: Vertical height of each step
Tread (going): Horizontal depth of each step

Divide the floor-to-floor height into equal risers no taller than the code allows; the number of treads is one less, because the upper floor forms the last step. The run is the treads times the tread depth, and the stringer is the diagonal. Blondel's old rule — two risers plus one tread close to an average stride of 63–65 cm — is still the best quick test of a comfortable stair.

Assumptions & sources

A straight flight with no landings or winders.
Stringer length is the diagonal of the total rise and the total run; allow extra for the top and bottom cuts.

1National Building Code of India 2016 (SP 7) — staircases: residential riser ≤ 190 mm, tread ≥ 250 mm — Bureau of Indian Standards
22018 IRC residential stair guide — R311.7.5 risers 7¾ in max, treads 10 in min, headroom 6 ft 8 in — Town of Timnath, Colorado (based on the International Residential Code)
3How to calculate staircase dimensions (Blondel's formula, 2R + T ≈ 63–65 cm) — ArchDaily

Calculator ID HOME-STAIRS-001 · version 1.0.0

Common questions

How many steps for a 10 ft (3 m) floor height?

With risers of about 170 mm, 3,000 mm needs 18 risers of 166.7 mm and 17 treads. Under the NBC's 190 mm limit the minimum is 16 risers.

What is a comfortable riser and tread?

Risers of 150–175 mm with treads of 250–300 mm. Check with Blondel's rule: two risers plus one tread should be about 600–650 mm.

Why is the number of treads one less than the risers?

The top riser steps you onto the upper floor, which acts as the last tread.