Power Calculators

🌬️ Room AC Size Calculator: Which Ton AC Do I Need?

1 ton or 1.5 ton? Find the right AC for your room — and what it will cost to run.

By the Power Calculators team Updated

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Enter details

sq ft or m² — instead of length × width.

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Fill in the details and click Calculate to see your results.

Formula at a glance

Room AC Size Calculator: AC size — Cooling load (BTU/h) ÷ 12,000, rounded to a standard size. Example: 12 × 12 ft bedroom, 3 star, 8 hours → AC size for your room: 1 ton
How the Room AC Size Calculator works: AC size — Cooling load (BTU/h) ÷ 12,000, rounded to a standard size

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📘 About the Room AC Size Calculator

Buying the wrong size is the most common AC mistake: too small and it runs flat out without cooling, too big and you pay more than you need. Room size matters most, but a top floor, strong sun, a very hot city or several people in the room push the size up.

Enter the room size and conditions. The calculator recommends a standard AC size and estimates the units and monthly running cost for the star rating you choose, using typical ISEER (energy-efficiency) values.

🧮 Formula

AC size
Cooling load (BTU/h) ÷ 12,000, rounded to a standard size
Units a day
Tons × 3.517 ÷ ISEER × hours × 0.8

✏️ Worked examples

12 × 12 ft bedroom, 3 star, 8 hours

You enter
Currency₹ Indian rupee
Measure infeet
Room length12
Room width12
Ceiling height10
Summer climateHot (35–40 °C)
FloorGround / middle floor
SunlightNormal
People usually in the room2
AC star rating3 star
Hours a day8 h
Electricity rate8 per unit
You get
AC size for your room1 ton
Cooling needed11,104 BTU/h (0.93 ton)
Power use (3-star, 8 h a day)5.6 units a day · 169 a month
Running cost₹1,351 a month at ₹8.00 a unit

1 ton; ₹1,351 a month at ₹8.00 a unit.

Top-floor 16 × 14 ft room, 5 star

You enter
Currency₹ Indian rupee
Measure infeet
Room length16
Room width14
Ceiling height10
Summer climateVery hot (above 40 °C — Delhi, Rajasthan, UP)
FloorTop floor (roof above)
SunlightVery sunny / west-facing
People usually in the room3
AC star rating5 star
Hours a day10 h
Electricity rate8 per unit
You get
AC size for your room2.5 ton
Cooling needed25,967 BTU/h (2.16 ton)
Power use (5-star, 10 h a day)14.1 units a day · 422 a month
Running cost₹3,376 a month at ₹8.00 a unit

2.5 ton.

🧭 How to use this calculator

What you enter

  • Currency
  • Measure in
  • Room length
  • Room width
  • Or floor area (optional)sq ft or m² — instead of length × width.
  • Ceiling height
  • Summer climate
  • Floor
  • Sunlight
  • People usually in the room
  • AC star rating
  • Hours a day (h)
  • Electricity rate (per unit)

What you get

  • AC size for your room
  • Cooling needed
  • Power use (3-star, 8 h a day)
  • Running cost

💡 Quick size guide

  • Up to 90 sq ft: 0.75 ton
  • 90–140 sq ft: 1 ton
  • 140–200 sq ft: 1.5 ton
  • 200–280 sq ft: 2 ton
  • Add half a ton for a top floor or very sunny room

❓ Frequently asked questions

Which AC is best for a 120 sq ft room?

A 1-ton AC is usually enough; choose 1.5 tons if it is on the top floor or gets afternoon sun in a very hot city.

How much does a 1.5-ton AC cost to run per month?

At 8 hours a day and ₹8 a unit, roughly ₹1,600–2,600 for a 5-star inverter and ₹2,500–3,500 for an older 3-star model.

Inverter or non-inverter AC?

Inverter ACs adjust their speed and use 30–50% less electricity over a season, so they are better if you use the AC more than a few hours a day.

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