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AC Tonnage Calculator

Air conditioner tonnage and what it costs to run. Tonnage is rounded to the sizes actually sold, and the running cost depends far more on the star rating than on the tonnage.

Also called: ac size calculator, air conditioner tonnage.

m²
m
Position
Recommended tonnage
0.75

0.75 ton for a 14 m² room, from a load of 3,090 BTU. At 5 stars and 8 hours a day that costs about 1,125.39 a month at 8 per unit. Rounded up to the nearest half ton sold. Do not round up further: an oversized unit cannot dehumidify.

Cooling load
3,090
Exact load in tons
0.26
Power draw
0.59
Units a month
140.7
Monthly running cost
1,125.39
Annual running cost
13,504.7
On the rounding
Rounded up to the nearest half ton sold. Do not round up further: an oversized unit cannot dehumidify.
On regulation
This is a sizing estimate. The applicable wiring or building regulation governs and overrides any figure here.
How this is calculated
Method and background

How this is calculated

The cooling load determines the tonnage, which then rounds to the half-ton sizes on the market. Running cost comes from the efficiency ratio implied by the star rating: a five star unit uses roughly a third less electricity than a three star for the same cooling, which over a few summers usually exceeds the price difference. Rounding up a size is the common instinct and the wrong one, since an oversized unit cannot dehumidify.

the star rating maps to an efficiency ratio, which converts cooling capacity into electrical draw
ISEER
Seasonal efficiency ratio

Worked examples

Each of these is asserted on every build. If a change to the engine ever moved one of these answers, the build would fail before the page could print it.

a 14 m² bedroom

Room area
14 m²
Ceiling height
3 m
Position
Middle floor
Occupants
2
Star rating of the unit
5
Hours of use a day
8
Electricity rate
8

Recommended tonnage0.75

42 m3 x 45 plus 1200

Open this example

a top floor room carries more load

Room area
14 m²
Ceiling height
3 m
Position
Top floor
Occupants
2
Star rating of the unit
5
Hours of use a day
8
Electricity rate
8

Recommended tonnage0.75

boundary: a 15 percent adjustment

Open this example

Method and limits

What it assumes

  • Indian star ratings mapped to typical seasonal efficiency ratios.

What it deliberately does not model

  • Star rating thresholds are revised periodically, so a rating is relative to its year.
  • Actual consumption depends on set temperature, insulation and outdoor conditions.

Formula version 1.0.0 · definition 1.0.0 · India · Report a problem with this calculator

Frequently asked questions

Is a 5 star unit worth the extra cost?
Usually, at typical usage. It uses around a third less electricity than a three star for the same cooling, and the difference compounds over the life of the unit.
Should I buy a larger tonnage to be safe?
No. An oversized unit reaches temperature fast, cycles off and never runs long enough to remove humidity, leaving the room cold and clammy.