Window Wind Load Calculator | IS 875 Part 3

1 Select City

City not listed?

m/s

2 Height of Window Above Ground

Or enter floor no:

Assumes 3 m per floor. Adjust if needed.

3 Surrounding Terrain Type (Cat 2 pre-selected — most common)

Cat 1 — Open / Coastal Open sea, flat coastal plains, airports, no obstructions Cat 2 — Open Land ✓ Most Common Scattered trees / small structures. Highways, farmland, open park land Cat 3 — Suburban / Industrial Well-wooded areas, towns, industrial areas (partially developed) Cat 4 — Dense City Large city centres, tall buildings > 25 m. Mumbai CBD, Connaught Place

4 Building Type / Importance

Affects k1 risk coefficient (Table 1, IS 875)

5 Cyclone-Prone Coastal Area?

6 Window Width

7 Window Height

8 Window / Opening Type (determines internal pressure coefficient Cpi)

Both +Cpi and −Cpi are checked; worst case governs as per Cl 7.3.2

🔧 Expert / Engineer Mode Override k1, k3, Kd, Ka, Kc, Cpe individually

Expert Overrides — IS 875 (Part 3): 2015

k1 — Risk Coefficient

Table 1, Cl 6.3.1. Auto: varies by Vb zone & class

k3 — Topography Factor

degrees upwind

Annex C, Cl 6.3.3. k3 range: 1.0 – 1.36

k3 — Manual Override (optional)

Overrides the topography selection above

Kd — Wind Directionality

Cl 7.2.1. Auto: 0.9 inland, 1.0 cyclone zone

Ka — Area Averaging Factor

Table 4, Cl 7.2.2. Auto: 0.70–1.0 per area

Kc — Combination Factor

Cl 7.3.3.13. Default 0.9 for cladding

Cpe — External Pressure Coefficient

Table 5, Cl 7.3.3.1. +0.8 windward wall

💡 Leave any field blank to use the auto-calculated value from IS 875. Filled values override auto-calculation and are shown in the result step table.

Input Reference Guide

What each input means and how to choose the right value

Input	What to enter	Impact on result
City	Your project location	Sets Vb (basic wind speed). E.g. Bengaluru = 33 m/s, Chennai = 50 m/s, Darbhanga = 55 m/s (highest in India)
Height	Height of window sill from ground level	Wind speed increases with height. 10th floor sees ~17% more wind than ground floor (Cat 2)
Terrain	What surrounds the building	Cat 1 (coastal) = most wind. Cat 4 (dense city) = buildings block wind. If unsure → Cat 2
Building Type	Use / importance of the building	Sets k1. Hospitals/schools: k1 up to 1.08. Temporary structures: k1 down to 0.67
Cyclone Zone	Is the building within 60 km of east coast or Gujarat coast?	Sets k4 (1.15–1.30) AND changes Kd to 1.0 as per Cl 7.2.1. Can increase pressure by 20–40%
Window Size	Width × Height in mm	Larger windows get a lower Ka (area averaging factor). Also gives total force in kgf
Opening Type	How sealed is the building	Open buildings have higher internal pressure. Worst of +Cpi and −Cpi is always used

📐

kPa vs kgf/m²

1 kPa = 1000 N/m² = 101.97 kgf/m². Aluminium system specs usually quote limits in kPa. Fabricators understand kgf/m² more intuitively. We show both.

🏙️

Typical Indian Values

Bengaluru / Pune residential: 0.5–0.8 kPa. Mumbai high-rise coastal: 1.2–1.8 kPa. Chennai / Visakhapatnam cyclone zone: can exceed 2.0–2.5 kPa.

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Disclaimer

This tool gives preliminary reference values only. All final facade and structural designs must be verified by a qualified engineer per IS 875 (Part 3): 2015.

Also try our 🔲 Sheet & Circle Weight Calculator →