AC Tonnage Guide — India 2026

The AC market in India just crossed 1 crore units/year. The single biggest mistake buyers make is either undersizing (AC runs flat-out, doesn't cool, bill still huge) or oversizing (compressor short-cycles, humidity control is poor, bill is even bigger). Here's the 2026 sizing rule, with monthly running cost numbers.

The 2026 sizing rule (ISEER-corrected)

• Up to 110 sq ft (small bedroom): 1.0 ton.
• 110–160 sq ft (standard bedroom): 1.5 ton.
• 160–230 sq ft (master bedroom / living): 1.8–2.0 ton.
• 230–300 sq ft (hall / open-plan): 2.0–2.5 ton.
• Above 300 sq ft: consider cassette or split the load across two ACs.

Add 10% tonnage for: top-floor rooms, west-facing glass, rooms with 4+ occupants, or kitchens.

Star rating economics in 2026

BEE's revised ISEER methodology (from Jan 2025) made star ratings stricter. A 2026 "3-star" is roughly what 2022 "4-star" used to be. For a 1.5 ton AC in a Delhi bedroom (8 hours/day, May–Sept):

• 3-star fixed-speed: ISEER 3.5, ~1,740 units/season, ₹13,920/year at ₹8/unit.
• 5-star fixed-speed: ISEER 4.1, ~1,490 units/season, ₹11,920/year.
• 3-star inverter: ISEER 3.75, ~1,620 units/season, ₹12,960/year.
• 5-star inverter: ISEER 4.7, ~1,295 units/season, ₹10,360/year.

The ₹10,000–15,000 price premium of a 5-star inverter over a 3-star fixed pays back in 3–4 summers for an 8 h/day user.

Inverter vs fixed-speed — when each wins

• Inverter wins when: you run the AC for 4+ hours at a stretch, you want lower sound, and your room is well-insulated.
• Fixed-speed is fine when: the AC runs only 1–2 hours at a time (guest rooms, office cabins), or your budget is tight.

Thermostat discipline cuts the bill 15–25%

• Set to 24 °C in summer. Every 1 °C lower = ~6% more consumption.
• Use sleep mode at night — it ramps the setpoint up by 1 °C/hour.
• Use fan mode after 4 AM — ambient usually drops below 25 °C.
• Close curtains 2 PM – 5 PM to block western sun.
• Clean filters once a month; clean coils yearly.

The running cost calculator shortcut

Daily units = Tonnage × 3.517 ÷ ISEER × hours × 0.7 (duty cycle). Multiply by your per-unit rate, then by 30. For a 1.5 ton 5-star inverter (ISEER 4.7) running 8 h/day at ₹8/unit: 1.5 × 3.517 ÷ 4.7 × 8 × 0.7 = 6.28 units/day → ₹50/day → ~₹1,500/month.

Compare your own AC's running cost vs alternatives with our appliance cost calculator.