Exhaust Fan Size Guide India 2026: 150mm vs 200mm vs 250mm

Short answer: a normal Indian bathroom needs a 150mm exhaust fan, a normal kitchen needs 200mm, and only a large or heavily-used kitchen needs 250mm. The number on the box is the sweep, not the hole you cut. Work out the airflow your room actually needs, then confirm the cut-out size fits the opening you already have — in that order.

Most people buy this the other way round. They pick a fan on price, drill, and find the fan either rattles in an oversized hole or refuses to clear the frame by 10mm. Both are avoidable in five minutes of arithmetic.

What does the mm number on an exhaust fan mean?

It is the sweep size — the diameter of the blade circle. 100mm, 150mm, 200mm, 250mm and 300mm are the sizes sold in India, and 150mm and 200mm cover the overwhelming majority of homes.

It is not the cut-out. The cut-out size is the square or round opening in the wall or window glass the fan body needs, and it is always larger than the sweep. A 150mm fan typically asks for a cut-out around 190x190mm; the exact figure is printed in the product specification, and it varies between brands by enough to matter. The Havells and RR Signature listings, for example, state their cut-out explicitly — read that line before you buy, not after.

So the rule is: sweep decides how much air moves, cut-out decides whether it physically fits.

How do I calculate the exhaust fan size I need?

Ventilation is measured in CMH — cubic metres per hour. The formula is one multiplication:

CMH needed = room volume in cubic metres x air changes per hour

Room volume is length x width x height in metres. Air changes per hour (ACH) is how many times you want the room's entire air replaced in an hour. The commonly used rules of thumb in Indian homes are:

Room	Air changes per hour
Bathroom / toilet	6–8
Kitchen (domestic cooking)	10–15
Utility / laundry	6–8

Worked example, a standard 5ft x 7ft bathroom with a 10ft ceiling:

• 1.5m x 2.1m x 3.0m = 9.45 cubic metres
• 9.45 x 8 ACH = about 76 CMH

That is comfortably inside what a 150mm fan delivers, which is why 150mm is the default bathroom answer in India.

Now a small kitchen, 8ft x 10ft x 10ft:

• 2.4m x 3.0m x 3.0m = 21.6 cubic metres
• 21.6 x 12 ACH = about 260 CMH

That is 200mm territory. Indian cooking — tadka, deep frying, pressure cooking — is why kitchens sit at 10–15 ACH while bathrooms sit at 6–8. The grease and steam load is simply higher.

150mm vs 200mm vs 250mm: which goes where?

150mm (6 inch) — bathrooms, toilets, small utility rooms, box rooms. Fits the cut-outs already present in most Indian flats. Quietest of the three at the same build quality, because a smaller blade at the same duty is doing less shouting. The SINGER Venti Q 150mm and Bajaj Maxio 150mm are both live in this size.

200mm (8 inch) — kitchens, larger bathrooms, rooms with a persistent smell or steam problem. This is the size to pick if you are ventilating anywhere food is cooked and you do not have a chimney. The Havells Ventil Air DX 200mm is the common pick here.

250mm and 300mm — large kitchens, commercial kitchens, garages, workshops. Overkill in a flat, and genuinely loud. If you are choosing between 200mm and 250mm for a home kitchen, 200mm is almost always the right call.

100mm — powder rooms and very small toilets only. Easy to under-size yourself here; check the CMH arithmetic first.

Should I buy a BLDC exhaust fan?

A BLDC exhaust fan runs a brushless DC motor instead of the induction motor in a conventional fan. It draws meaningfully less power for the same airflow and usually runs quieter. A conventional 150mm fan sits around 22–30W; a BLDC equivalent such as the atomberg Studio 150mm BLDC runs well under that.

Whether it pays back depends entirely on runtime. A bathroom fan that runs 20 minutes a day will never recover the price difference in electricity. A kitchen fan that runs three hours a day, every day, is a different calculation. Buy BLDC for the noise, treat the power saving as a bonus — that is the honest way round for domestic use.

Exhaust fan or chimney for the kitchen?

They are not substitutes. A chimney sits directly over the hob and captures grease and smoke at the source. An exhaust fan sits in the wall and changes the air in the whole room. A chimney handles what comes off the pan; an exhaust fan handles the heat and residual smell that the chimney misses. Small kitchens with light cooking can get by on a good 200mm exhaust fan alone. Anything heavier wants both. We covered the full trade-off in kitchen chimney vs exhaust fan.

What else actually matters when buying?

Cut-out size. Repeated because it is the single most common return reason. Measure the existing opening before ordering.

Mounting type. Wall-mount, window-mount and ceiling-mount are different products. A window-mount fan expects a glass pane cut-out; a wall-mount expects masonry and a duct or a straight-through opening.

Shutters. Auto-shutters close when the fan is off and keep insects, dust and back-draught out. On a bathroom fan facing a duct shaft, this is not optional.

Rust-proof body. Bathrooms are humid by definition. A plastic or powder-coated rust-proof body outlives a bare metal one in Indian conditions, particularly in coastal cities.

Noise. A cheap fan at the correct size is quieter than an expensive fan at the wrong size. Over-sizing to "be safe" is how people end up with a fan they never switch on.

Quick reference

Room	Typical size	Typical CMH need
Small toilet	100–150mm	50–70
Standard bathroom	150mm	70–100
Large bathroom	150–200mm	100–150
Small kitchen	200mm	200–300
Large kitchen	200–250mm	300–450

Work the arithmetic for your own room rather than copying the table blindly — a 12ft ceiling changes the answer by 20%.

Where to buy

Exhaust fans discount heavily and unpredictably; a 150mm fan can sit anywhere between ₹650 and ₹1,700 depending on brand, motor and week. Current live prices across brands are on our exhaust fan and appliance offers page, and the model-by-model comparison is in best exhaust fans for kitchen and bathroom.

Get the sizing right first. A ₹690 fan in the correct size beats a ₹1,700 fan in the wrong one, every time.