AC tonnage for Indian rooms: the sizing rules that hold at 45 °C

The Indian working rules, tested against the plains’ furnace summers: 0.8 ton to about 100–110 sq ft, 1 ton to 130–150, 1.5 tons to 180–220, 2 tons to 250–300 — assuming 10 ft ceilings, moderate sun and a non-top-floor room. One ton = 12,000 BTU/h = 3.517 kW of cooling; the vocabulary descends from the ice-melting capacity that once defined refrigeration.

The corrections that matter in India

• Top floor under a concrete roof: +0.5 ton equivalent — roof slabs soaked all day radiate all night; this is the most under-weighted factor in Indian sizing.
• West-facing windows without shading: half a size up, or invest ₹2,000 in external shading first.
• 45 °C+ cities (Nagpur, Delhi, Gwalior belt): check rated cooling at high ambient — capacity at 43–46 °C, published for Indian-market models — rather than adding tonnage blindly; a unit that holds capacity at 46 °C beats a bigger unit that derates.
• Kitchens, dense occupancy, server corners: add ~0.1 ton per extra person beyond two, more for cooking heat.

The oversizing trap, Indian edition

A 2-ton unit in a 1-ton bedroom hits 24 °C in minutes, shuts down before dehumidifying, and delivers the clammy-cold room every monsoon knows — while its start-stop cycling burns the efficiency an inverter was bought for. Inverters mitigate but do not repeal the rule: they modulate down to 30–40% of rated capacity, so a modest oversize is absorbed, a doubling is not. When stuck between sizes for a humid city, take the smaller inverter; for a dry scorcher’s top floor, the larger.

Frequently asked questions

Does higher tonnage mean higher electricity bills?

Not if sized right: a correctly-sized unit cycling gently often uses less than an undersized one running flat-out forever, and less than an oversized one start-stopping. The bill follows the room’s heat load and the ISEER, not the nameplate tons.

My dealer sizes by « 1.5 ton for any bedroom » — is that wrong?

It is lazy but often lands near the truth for the classic 12×12–14×12 Indian bedroom. The failures happen at the edges: small AC-first rooms (0.8–1 ton suffices) and big halls or top floors (needs real calculation). Measure your room; the rules above take two minutes.

Can one 2-ton AC cool a hall plus an open bedroom?

An open-plan hall, yes, if the total area fits the rating. Through a doorway, poorly — air throw dies at doorways, and the far room settles 4–6 °C warmer. Separate rooms deserve separate (smaller) units.

More India guides: Air cooler vs AC in India: the honest decision, city by city · How evaporative cooling works: the physics behind the desert cooler · BEE star ratings and ISEER: reading the Indian energy label · Inverter ACs explained: why the compressor that never stops saves money · Voltage stabilizers for ACs: still necessary, or legacy habit?.