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AC Tonnage Calculator

Right-sizing matters: undersized AC runs all day and never cools; oversized AC short-cycles and wastes energy. Rule of thumb: 1 ton per 130 sqft, adjusted for climate and floor.

150 sqft
10 ft
2
Recommended AC
1.5 ton
Calculated need: 1.33 tons (15923 BTU/hr)

Inverter or non-inverter both fine; inverter still saves 15-20%.

How it works

Required cooling capacity = floor area × heat-load factor, adjusted for ceiling height, top-floor exposure, west-facing windows, kitchen heat and number of occupants. 1 ton of AC = 12,000 BTU/hr ≈ 3,517 watts of cooling. The classic Indian baseline of 1 ton per 130 sqft assumes a normal climate, 9-ft ceiling and 2 occupants — Chennai and Ahmedabad need ~15% more, hilly Bangalore can get away with ~15% less.

Worked example

A 12 ft × 14 ft Pune bedroom (168 sqft) on the 2nd floor of a 4-storey building, west wall, 2 adults: base 168 ÷ 130 = 1.29 ton, +0.1 for west sun = 1.39 ton — round up to a 1.5 ton split. A 5-star inverter at this size pulls ~1,100 W; running 8 hours/day in May at ₹8/kWh costs roughly ₹2,650/month. Undersizing to 1 ton would run the compressor flat-out and cost more.

When to use this

  • Before buying during the April-May summer-sale window in Delhi, Mumbai, Bangalore
  • Replacing a 10-year-old non-inverter unit to right-size for a 5-star BEE-rated inverter
  • Specifying multiple ACs in a new flat — common to undersize the master bedroom

Pair this with our unit converter if you have room dimensions in metres, and use the running-cost figures from a 5-star inverter at your local discom tariff before purchase.

FAQ

What ISEER rating is right?

5-star: 4.5+ ISEER, ~₹600-900 / month for 1.5T at 8 hrs/day in Delhi summer. 3-star: 3.5-4.0 ISEER, 30% higher running cost.

Window AC or split?

Split — quieter, more efficient (modern inverters), better aesthetics. Window is cheaper upfront and easier to install but rarely sold above 1.5 ton. For long-term, split is the standard.

Is buying an AC worth it for < 4 months of summer?

Up to 6 weeks: probably not. 6 weeks - 3 months: marginal — air cooler often suffices. 3+ months: yes, especially Delhi/Rajasthan/Hyderabad.