What AC size do you need? Room size to tonnage, explained

Last updated: 6 August 2026

A 1.5-ton AC in a 120 sq ft bedroom is not "extra cooling to be safe". It is a unit that hits your set point too quickly, switches off before it has pulled moisture out of the air, and leaves you with a room that is cold and clammy at once. Buying one size up is the most common sizing mistake in India, and it is worth understanding before you spend ₹25,000 or more.

AC tonnage is a measure of heat removal, not the weight of the machine. One ton of refrigeration is the cooling effect of melting one short ton of ice over 24 hours — roughly 3,517 watts of heat moved out of your room every hour.

Which AC tonnage do you need for your room size?

For most Indian homes, a room up to 100 sq ft needs about 0.8 TR, 100–150 sq ft needs 1.0 TR, 150–200 sq ft needs 1.5 TR, and 200–250 sq ft needs 2.0 TR. This assumes a standard ceiling height, one or two occupants, and a room that is not directly under an exposed roof. Treat it as a starting point, then adjust for the conditions below.

A 150 sq ft room — a common Indian master bedroom at roughly 12 ft × 12 ft — sits exactly on the boundary between 1.0 TR and 1.5 TR. That boundary is where the rest of this article matters.

Why the room-size chart alone gets it wrong

The chart assumes an average room. Five conditions push a room up a size. If two or more apply to you, size up from the chart; if none apply, the chart figure is correct and going higher costs money for nothing.

• Top floor or exposed roof. Direct sun on the slab above is the largest single load most Indian rooms carry.
• West-facing windows. Afternoon sun through unshaded glass adds heat exactly when you want the room coolest.
• More than two people regularly in the room. Each adult adds roughly 100 W of heat.
• Kitchen or heat-producing equipment. A desktop, a large TV, or cooking nearby all count.
• Ceiling above 10 ft. The chart is volume in disguise; a tall ceiling is a bigger room.

1 Ton vs 1.5 Ton: the decision most buyers actually face

The practical difference between 1 Ton and 1.5 Ton is 1,400 W of cooling capacity and 375 W of rated power draw. For a room under 150 sq ft on a middle floor, 1 Ton is sufficient and cheaper to run. For 150–200 sq ft, or a top-floor room anywhere in that range, 1.5 Ton is the safer choice.

These are the rated figures for the current Ecozen Smart AC (BEE 2026 model), taken from the manufacturer's specification sheet rather than derived from efficiency ratings:

To turn this into a bill, multiply the rated draw by your hours of use and then by your own electricity tariff. A 1.5 Ton unit running 8 hours at full rated draw uses about 11 kWh a day — but that is an upper bound, not the expected figure. An inverter compressor throttles down once the room is cool, and the same unit has a floor of 505 W. Real consumption sits between those two numbers, nearer the lower one in a correctly sized room. We have not printed a rupee figure here on purpose: tariffs differ by state and by slab, so use your own latest bill.

What oversizing and undersizing actually cost you

Undersizing shows up as an AC that runs continuously and never quite reaches the set point on the hottest days. Oversizing is less obvious and far more common: the unit cools the air fast, satisfies the thermostat, and stops — before it has run long enough to condense humidity out of the room.

That short-cycling is what people are describing when they say a room feels "cold but sticky". It also means more compressor starts, which is the hardest thing a compressor does. On a fixed-speed AC the effect is severe. On an inverter unit it is softened, because the compressor can slow instead of stopping — but a genuinely oversized inverter unit still spends its life at the bottom of its range, which is not where it works best either.

Where convertible modes change the answer

Convertible capacity lets an inverter AC cap its compressor at a percentage of rated output, so one machine can behave like a smaller one when the room is lightly loaded. On the Ecozen Smart AC in 1.5 Ton and above, the steps run 40, 60, 80, 90, 100, 110 and 115 percent, plus a 50 percent economy mode. The 1 Ton uses a slightly different set of steps.

This genuinely helps at the boundary cases. If your room is 150 sq ft and you are torn between 1.0 and 1.5 TR, a convertible 1.5 TR unit run at 60–80 percent on ordinary nights gives you the smaller machine's behaviour, with headroom for the worst week of May. What it does not do is rescue a badly oversized purchase — a 2 TR unit in a 120 sq ft room is still a 2 TR unit with a 530 W floor.

What else to check before you buy

Tonnage decides whether the room gets cool. These four decide what the next five years look like. All figures below are for the current Ecozen Smart AC (BEE 2026 model); the earlier model year differs on several of them.

Whether that 56 °C ceiling matters to you depends on where you live. The India Meteorological Department publishes regional temperature and heatwave data, which is a better guide to your worst-case week than any national average.

Check the warranty separately from the specification, because it varies by model year. The current Ecozen Smart AC carries five years of cover — one year from Ecozen and four years of extended warranty from Acko, with no deductible at claim time. The full terms, including exclusions, are on the extended warranty page.

For star ratings and the ISEER bands themselves, the authoritative source is the Bureau of Energy Efficiency, not a retailer's comparison chart.

Frequently asked questions

Which AC is best for a 150 sq ft room?
A 150 sq ft room sits on the 1.0 TR / 1.5 TR boundary. Choose 1.0 TR if it is a middle-floor room with shade and one or two occupants; choose 1.5 TR if it is on the top floor, has west-facing windows, or is used by three or more people.

1 ton AC kitne square feet ke liye hai?
A 1 ton AC suits a room of roughly 100 to 150 square feet at standard ceiling height. Above 150 sq ft, or on a top floor, move up to 1.5 ton.

Is a bigger AC always better?
No. An oversized AC cools the air quickly and shuts off before it has removed humidity, leaving the room cold and damp. It also costs more to buy and cycles the compressor harder.

Does an inverter AC need different sizing?
Sizing starts the same way. An inverter unit is more forgiving at the boundaries because it can throttle down instead of switching off, but the room-size chart is still where you begin.

1.5 ton AC kitni bijli khaata hai?
The current Ecozen 1.5 Ton draws 1,380 W at its rated point and throttles down to 505 W. Eight hours at the rated draw is about 11 kWh; real use in a correctly sized room sits below that. Multiply by your own tariff for a rupee figure.

Can one AC cool two rooms?
Not reliably. Cooling depends on air circulating within an enclosed space, so a single unit serving two rooms through a doorway will cool the room it is in and underperform in the other.

Choosing your Ecozen Smart AC

The Ecozen Smart AC comes in 1 Ton, 1.5 Ton, 1.6 Ton and 2 Ton, all 3-Star BEE 2026 with ISEER 4.41, R32 refrigerant and EcoSphere app control. Match your room to the chart above, adjust for top floor and sun exposure, then pick from the Ecozen Smart AC range. If you want the engineering behind the unit rather than the sizing, the Smart AC overview covers the inverter, the coil and the app.