What is Blondel's formula and why is it important?

Blondel's formula states that 2R + T should equal 600–640 mm for comfortable staircase design (R = riser height, T = tread depth). It ensures the step proportions match the natural human stride. A result outside 600–640 mm means the staircase may feel uncomfortable or unsafe to use.

What is the standard staircase size for a Pakistani house?

For a typical Pakistani house with 3m floor-to-floor height: 20 risers of 150mm each, 250–275mm tread depth and 1000–1200mm stair width. This gives a pitch of about 29°–31°, comfortable for daily use, needing roughly 19 × 270 = 5130mm ≈ 5.2 metres of horizontal space.

What is the minimum headroom clearance for a staircase?

Minimum headroom above any stair tread must be at least 2100mm (2.1m) measured vertically, throughout the whole staircase. Under IS 456 and the Pakistan National Building Code, 2100mm is the absolute minimum; 2200–2400mm is recommended for comfortable use.

Architecture & Structural

Staircase Calculator

Calculate number of steps, riser height, tread depth, going, pitch angle, and concrete volume for RCC staircases — with IS, BS, and standard design checks.

RCC Staircase Calculator

Steps · Riser · Tread · Pitch Angle · Concrete Volume

Staircase Components: Riser (vertical), Tread (horizontal), Going = Tread × No. of steps

Floor-to-Floor Height (mm) Total vertical height to climb

Stair Width (mm) Min 900mm residential, 1200mm public

Preferred Riser Height R (mm) Standard: 150–175 mm. Max 200 mm (IS)

Preferred Tread Depth T (mm) Standard: 250–300 mm. Min 200 mm (IS)

Waist Slab Thickness (mm) Typically Span/20 to Span/25

Landing Length (mm) Top and bottom landing length

Nosing (mm) Overhang of tread beyond riser

Stair Type

Staircase Results

Calculated

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nos

No. of Steps

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Actual Riser

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Total Going

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Pitch Angle

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2R+T Check

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m³

Concrete Vol

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m²

Floor Area Used

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Slope Length

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Staircase Design Rules & Formulas

Blondel's Formula — Comfort Check

    Blondel's Rule:  2R + T = 600 to 640 mm  (ideal comfort)
    Number of Risers = Floor Height ÷ Riser Height
    Number of Treads = Number of Risers − 1
    Total Going     = Tread × Number of Treads
    Pitch Angle θ   = arctan(R ÷ T)  degrees
    Slope Length    = √(Going² + Floor Height²)
    Concrete Volume = (Waist + R/2) × Width × Slope Length / 1000³
  

Per IS 456 and NBC of Pakistan: Riser ≤ 190mm · Tread ≥ 250mm · Pitch ≤ 38° · 2R+T = 550–700mm · Headroom ≥ 2100mm

Standard Staircase Dimensions by Building Type

Building Type	Min Width	Riser	Tread	Pitch
Residential House	900 mm	150–175 mm	250–300 mm	27°–35°
Apartment Building	1200 mm	150–175 mm	260–300 mm	27°–34°
Commercial Building	1500 mm	150–165 mm	280–320 mm	25°–30°
Public Building	1800 mm	130–150 mm	300–340 mm	21°–27°
Industrial / Factory	1000 mm	175–200 mm	230–260 mm	34°–41°
External/Fire Escape	750 mm	175–200 mm	220–250 mm	35°–42°

Frequently Asked Questions

Blondel's formula states that 2R + T should equal 600–640 mm for comfortable staircase design (where R = riser height, T = tread depth). This formula ensures the step proportions match the natural human stride length. A result outside 600–640 mm means the staircase may feel uncomfortable or unsafe to use.

For a typical Pakistani residential house with 3m floor-to-floor height: 20 risers of 150mm each, with 250–275mm tread depth, 1000–1200mm stair width. This gives a pitch of approximately 29°–31°, which is comfortable for daily use. The total horizontal space needed is approximately 19 × 270 = 5130mm ≈ 5.2 meters.

Minimum headroom clearance above any stair tread must be at least 2100mm (2.1m) measured vertically. This applies throughout the entire length of the staircase. Under IS 456 and the Pakistan National Building Code, 2100mm is the absolute minimum; 2200–2400mm is recommended for comfortable use.