Bathroom Exhaust Fan Calculator
Enter your bathroom size, how heavily it is used and the duct run to outside. Get the airflow you need in CMH and CFM, plus a recommended fan size and diameter. Windowless bathrooms need mechanical ventilation under NBC 2016 — indicative India 2026, confirm locally.
Your bathroom & duct
Room volume is 8.9 m³ (315 ft³). We size for 10 air changes per hour and oversize by 7% for a 3.5 m equivalent duct run (each bend ≈ 1.5 m). A longer, kinked duct needs a stronger fan to move the same air.
Airflow required
0 CMH
that is 0 CFM — pick a fan rated 120 CMH or higher (100 mm class)
Required airflow
95 CMH
56 CFM
Recommended fan
120 CMH
round up to a stocked size
Fan diameter class
100 mm
≈ 4" duct
Indicative price
₹700–2,500
budget → premium, confirm locally
Required airflow (amber) vs common fan ratings in CMH; teal is the smallest stocked fan that clears it. Indicative — confirm with your vendor.
Get the ventilation right
Discuss fan type, placement and duct routing for this bathroom with DesignAI.
Estimates are indicative and round up to common fan ratings. Actual delivered airflow depends on the duct diameter, length, bends and the fan's pressure curve — a fan's rated CMH is measured with no duct, so always keep some headroom. For windowless toilets and bathrooms, NBC 2016 requires mechanical ventilation; confirm the fan capacity, duct routing and electrical provision with your contractor before buying.
Frequently asked questions
- How does the bathroom exhaust fan calculator work?
- It first finds your room volume from length, width and ceiling height, then multiplies that volume by the air changes per hour for your usage level to get the airflow you need. Windowless rooms get an extra allowance, and the figure is then oversized a little for the duct run and bends. The result is shown in CMH and CFM with a recommended fan rating.
- What air changes per hour should I choose for my bathroom?
- A light-use powder room or guest WC is fine near eight air changes per hour, a standard family bathroom around ten, a shower-heavy room about twelve, and a shared or very intense bathroom up to fifteen. If the room has no openable window, add roughly three more because there is no natural airflow to help clear steam and odour.
- How accurate is this exhaust fan size and what should I verify?
- Treat it as an indicative planning figure. A fan's rated CMH is measured with no duct attached, so real delivered airflow drops with longer runs, bends and grille resistance, which is why the tool keeps headroom. For windowless toilets and bathrooms, NBC 2016 requires mechanical ventilation. Confirm the final fan capacity, duct routing and electrical provision with your contractor and the manufacturer data.
Related Guides — Deep-dive reading
Bathroom Exhaust Fan India: CFM Sizing, Wall vs Ceiling vs Inline, Ducting, Sones & Cost
How to specify a bathroom exhaust fan that actually clears steam in an Indian home — sizing by CFM from room volume and air changes, choosing wall, ceiling or inline, ducting it to outside air (never into a false-ceiling void), and picking backdraft-damper, humidity-sensor and timer models at the right noise and IP rating.
BathroomsBathroom Ventilation India: The Complete Guide to Moisture, Mould, NBC 2016 Air Changes & Windowless Solutions
Why bathroom ventilation matters more than any fitting in an Indian home — how moisture, mould and odour build up, natural versus mechanical options, what NBC 2016 actually requires, how to size a fan by air changes and CFM, and how to ventilate a windowless bathroom that stays dry through the monsoon.
BathroomsExhaust Fan vs Natural Ventilation for Indian Bathrooms: Which Actually Keeps It Dry? (India)
A fair, room-by-room verdict on mechanical exhaust fans versus natural window-and-ventilator airflow — moisture and odour removal, the windowless reality, monsoon humidity, running cost, what NBC 2016 demands, and why the honest answer for most Indian bathrooms is 'both'.
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Gauge condensation and mould risk in a bathroom and the ventilation needed to control it — a 0-100 risk score with drivers and fixes.
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