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AC Tonnage Calculator

Find the right AC size in ton for your room, and estimate the monthly electricity bill.

Room size in
ft
ft
ft
Most Indian flats have 9.5–10 ft ceilings.
Floor
A roof in direct sun adds a lot of heat: +20%.
Sun on the walls
Walls or big windows in afternoon sun: +10%. Well shaded: −10%.
I know my AC's
Printed on the BEE star label. Higher is more efficient; inverter 5-star ACs have the highest ISEER.
%
An AC rarely runs flat out. ~60% is typical for a hot day; use 80–90% for a sun-baked room, 40% for night use.
h
days
₹/unit
Your bill's per-unit rate including charges; domestic tariffs differ by state and slab.
Recommended AC size
1 ton
Cooling load 0.90 ton (10,800 BTU/h)
Room area
120 sq ft
11.1 m²
Cooling needed
3.17 kW
Units per month
113kWh
0.47 units per hour of use
Monthly bill (AC)
₹900
for a 1 ton AC
Summer (4 months)
₹3,601
Rule-of-thumb estimate: 10,800 BTU/h ≈ 0.90 ton ≈ 3.2 kW of cooling (1 ton = 12,000 BTU/h = 3.517 kW). Rooms with poor insulation, lots of glass or a hot kitchen next door may need one size up.
Where the heat comes from
ItemRuleBTU/h
Floor area120 sq ft × 80 BTU/h per sq ft9,600
Ceiling height10.0 ft vs 10 ft0
Top floorNone0
Sun on wallsNone0
People2 × 600 BTU/h1,200
Other heat sourcesNone0
Total cooling load÷ 12,000 BTU/h per ton = 0.90 ton10,800

Runs entirely in your browser. Nothing you type or upload is sent to us or stored.

Results are for general guidance. Please check anything important before relying on it. Terms of use

How to Use

  1. Enter the room's length, breadth and ceiling height in feet or metres.
  2. Pick your city climate, whether the room is on the top floor, how much sun its walls get, the number of people and any heat sources such as an open kitchen.
  3. Read the recommended AC size in ton. The table below shows how each item adds to the cooling load.
  4. For the running cost, enter your AC's ISEER, the units per year from its BEE label, or its power in watts.
  5. Set your hours of use and electricity rate to see the monthly units and bill. Everything updates as you type.

How to choose the right AC size for your room

An AC's "ton" is a measure of how much heat it can remove from a room, not its weight. The size you need depends mostly on how much heat gets into the room: through the walls, roof and windows, from the people inside and from appliances. If the AC is too small, it runs flat out on hot afternoons and never quite cools the room. If it's too big, it costs more to buy and a non-inverter model keeps switching on and off, which leaves the air damp.

Ton, BTU and kW

1 ton of refrigeration = 12,000 BTU per hour = 3.517 kW of cooling

The ton comes from the heat needed to melt one short ton of ice in 24 hours. Spec sheets in India often give the cooling capacity in watts: a "1.5 ton" split AC is usually rated at around 5,000–5,300 W of cooling. That's cooling output, not the electricity it uses.

The method this calculator uses

Load (BTU/h) = area (sq ft) × climate factor × (ceiling height ÷ 10 ft)
  × (1 + 20% if top floor) × (1 ± 10% for sun or shade)
  + 600 per person + 1,000 for TV/computer or 4,000 for a kitchen
Tons = load ÷ 12,000, rounded up to a common AC size

The climate factor is 80 BTU/h per sq ft for hot, dry cities, 75 for hot, humid coastal cities and 60 for milder places like Bengaluru. These are our own calibration, chosen so the results match the sizing charts Indian AC brands publish. They aren't an official standard. The per-person (600 BTU/h) and kitchen (4,000 BTU/h) additions and the ±10% for sun come from the US ENERGY STAR room-AC sizing guide.

Worked example

A 12 × 10 ft bedroom (120 sq ft) in Delhi with a 10 ft ceiling, on a middle floor, used by 2 people:

  • Room: 120 × 80 = 9,600 BTU/h
  • People: 2 × 600 = 1,200 BTU/h
  • Total: 10,800 BTU/h ÷ 12,000 = 0.9 ton → a 1 ton AC

Put the same room on the top floor under a sunlit roof and the load goes up to 12,720 BTU/h (1.06 ton). That's just over 1 ton, so a 1.5 ton AC is the safer choice.

Typical sizes (middle floor, 2 people, hot city)

Room sizeExampleSuggested AC
Up to about 140 sq ft10 × 12 ft bedroom1 ton
About 140–220 sq ft12 × 15 ft bedroom1.5 ton
About 220–300 sq ft14 × 18 ft living room2 ton
Over 300 sq ftLarge hall2.5 ton+ or two ACs

A top floor, west-facing glass or a kitchen nearby can push a room up one size.

Estimating the electricity bill

The BEE star label on every AC sold in India shows its ISEER (Indian Seasonal Energy Efficiency Ratio) and an annual energy figure in units (kWh). That annual figure assumes 1,600 hours of use a year, so dividing it by 1,600 gives the units used per hour. If you only know the ISEER, the calculator uses cooling capacity × average load ÷ ISEER. The average load is an adjustable assumption, because an AC rarely runs at full power for a whole hour. Multiply by your hours of use and your tariff to get the monthly cost.

Tariffs are set separately by each state and change with your slab, so use the per-unit rate from your own bill, including fixed and fuel charges.

Tips to cut the cooling load

  • Set the AC to 24–26 °C. Each degree lower makes it work noticeably harder.
  • Use curtains or reflective film on west and south windows, and keep doors closed.
  • On a top floor, white reflective roof paint or terrace shading reduces heat from the roof.
  • Clean the filters every few weeks in summer.

For offices, shops and big halls, ask an HVAC engineer to calculate the heat load properly. This calculator gives a rule-of-thumb estimate for homes.

Frequently Asked Questions

In most Indian cities, a 1 ton AC is enough for a 120 sq ft bedroom (about 10 × 12 ft) on a middle floor with two people. If the room is on the top floor, faces the afternoon sun or has a kitchen nearby, choose 1.5 ton.

1 ton of cooling is 12,000 BTU per hour (3.517 kW), so a 1.5 ton AC is 18,000 BTU per hour, or about 5.3 kW of cooling. Many 1.5 ton split ACs sold in India are rated a little lower, at around 5 kW. Check the cooling capacity on the spec sheet.

Not always. An oversized non-inverter AC cools the room quickly, then switches off before it has removed much moisture, so the room feels cold and clammy. It also costs more to buy. Inverter ACs handle extra capacity better because they slow down instead of switching off, but buying much more capacity than you need is still wasted money.

It depends on the AC's efficiency, how hot it is outside and the thermostat setting. BEE labels give the annual energy for 1,600 hours of use. Divide that by 1,600 to get the units per hour. For example, a label showing 900 units a year works out to about 0.56 units per hour. Real use is higher on very hot days and lower at night.

Usually, yes. A roof in direct sun heats the room from above all afternoon and into the night. This calculator adds 20% to the room's load for a top floor. Reflective roof paint or shading on the terrace can reduce it.

ISEER (Indian Seasonal Energy Efficiency Ratio) is the cooling an AC delivers over a typical Indian cooling season, divided by the electricity it uses. Higher is better. The Bureau of Energy Efficiency (BEE) sets the ISEER bands for each star rating and revises them from time to time, so compare the ISEER numbers rather than just the stars.