Stair Calculator

Stair Calculator

Work out the number of steps, riser height, going, stringer (waist slab) length and stair angle for a straight flight of stairs, then get the RCC concrete volume and material quantities for the waist slab and steps.

Stair Dimensions

Total Rise / Floor-to-Floor Height (mm): Target Riser Height (mm): Going / Tread Depth (mm): Staircase Width (m): Waist Slab Thickness (mm): Available Headroom (mm, optional):

The riser height is auto-adjusted so a whole number of equal steps exactly covers the total rise; the value you enter is a target, not a fixed figure. Leave Width and Waist Thickness empty to use 1.0 m and 150 mm.

Material Estimate (Optional)

Concrete Mix Grade: M15 (1 : 2 : 4) M20 (1 : 1.5 : 3) M25 (1 : 1 : 2) Wastage Allowance (%):

NUMBER OF STEPS (RISERS)

--

ACTUAL RISER HEIGHT

--mm

NUMBER OF TREADS (GOINGS)

--

Going = -- mm each

TOTAL RUN

--m

STAIR / RAIL ANGLE

--°

STRINGER / WAIST SLAB LENGTH

--m

Inclined length, floor to floor

CONCRETE VOLUME (WAIST + STEPS)

--m³

CEMENT REQUIRED

--bags

Comfort & Good-Practice Checks

Riser height (150–190 mm typical residential range)--

Going / tread depth (250–300 mm typical range)--

Blondel comfort formula, 2×Riser + Going (550–700 mm)--

Headroom clearance (commonly 2100–2200 mm minimum)--

Reference Guide: Stair Geometry & RCC Quantities

1. Steps, Riser and Going

Number of Risers = Round(Total Rise / Target Riser Height)
Actual Riser Height = Total Rise / Number of Risers
Number of Treads = Number of Risers − 1

The riser height is adjusted so a whole number of equal steps exactly reaches the floor above; this is why the actual riser can differ slightly from the target you enter. This calculator assumes the top riser lands flush with the upper floor, so the tread count is always one less than the riser count.

2. Total Run, Stringer Length and Angle

Total Run = Number of Treads × Going
Stringer Length = √(Total Rise² + Total Run²)
Stair Angle = arctan(Riser / Going)

A comfortable stair angle for regular use is generally between 30° and 38°. A steeper angle saves floor space but feels closer to a ladder; a shallower angle is easier to climb but needs a longer total run.

3. Comfort Check: Blondel's Formula

Blondel's formula relates riser and going to a comfortable stride length: 2 × Riser + Going should fall roughly between 550 mm and 700 mm, with 600–640 mm generally considered ideal. A value below this range gives a cramped, steep stair; a value above it gives an unusually flat, space-hungry stair.

4. RCC Waist Slab and Step Concrete Volume

Waist Slab Volume = Waist Thickness × Width × Stringer Length
Step (Wedge) Volume = 0.5 × Riser × Going × Width × Number of Risers
Total Concrete Volume = Waist Slab Volume + Step Volume

The waist slab is the sloping structural slab that follows the underside of the stair, exactly like the stringer in a timber stair; the steps sit on top of it as triangular wedges. Material quantities (cement, sand, aggregate) follow the same dry-volume method as the general Concrete Calculator: Dry Volume = Wet Volume × 1.54, split by the mix ratio and converted using 0.0347 m³ per 50 kg cement bag.

5. Headroom

Headroom is the clear vertical distance from any tread's nosing to the underside of the structure above (a landing, beam or slab edge) directly above it. Most building codes call for a minimum of roughly 2100–2200 mm; always confirm the exact figure required by the code and occupancy that applies to your project.