AC electricity cost calculator
Enter the tonnage, the ISEER on the BEE label, your hours and your tariff to estimate what an AC costs to run. The page shows an example result even without JavaScript.
Quick answer
With the example values (a 1.5 ton AC, ISEER 4.5, 8 hours a day for 150 days, around ₹8 a unit), the estimate is about 1.17 units an hour, ₹75 a day and ₹11,254 a year. Change the boxes to match your AC and your bill. The formula is: units per hour = tonnage × 3.517 ÷ ISEER, and cost = units × hours × tariff.
Calculate the running cost
Estimated cost
- Electricity per hour
- 1.17 units
- Per day
- 9.38 units, ₹75
- Per 30 days of use
- ₹2,251
- Per year (150 days)
- 1,407 units, ₹11,254
This assumes the AC cools at its full rated capacity for every hour you entered. A real AC eases off once the room is cool, so your bill is usually lower. Treat it as an upper-end estimate.
Same inputs, different ISEER
| ISEER | Units per hour | Cost per year |
|---|---|---|
| 3.5 | 1.51 | ₹14,470 |
| 4.0 | 1.32 | ₹12,661 |
| 4.5 | 1.17 | ₹11,254 |
| 5.0 | 1.06 | ₹10,129 |
| 5.5 | 0.96 | ₹9,208 |
| 6.0 | 0.88 | ₹8,441 |
The formula
1 ton of cooling is 12,000 BTU an hour, which is 3.517 kW of heat removed. ISEER is the cooling an AC delivers over a season divided by the electricity it uses, so the electricity it draws is the cooling divided by the ISEER.
Units per hour = tonnage × 3.517 ÷ ISEER
Cost = units per hour × hours × tariff per unit
Example: 1.5 × 3.517 ÷ 4.5 = 1.17 units an hour. Eight hours is 9.38 units. At around ₹8 a unit that is ₹75 a day.
The estimate assumes the AC cools at its full rated capacity for every hour. It does not model the thermostat, room temperature or the fan. It is an upper-end figure, so use it to compare ACs and tariffs rather than to predict your exact bill.
What ISEER is
BEE, the Bureau of Energy Efficiency, defines the Indian Seasonal Energy Efficiency Ratio as the ratio of the total annual amount of heat the equipment removes from the indoor air when cooling in active mode to the total annual amount of energy it consumes in the same period. The BEE label shows it, together with the label period, the star level and the electricity use in units per year.
A higher ISEER means less electricity for the same cooling. Stars are bands of ISEER values, and the bands have been revised, so enter the ISEER and not the star. Our 3 star vs 5 star guide lists the bands we could read in the official notifications.
Tonnage helper: which size for my room?
Suggested size: 1.5 ton
This is the size for your area, with no step-up for sun or crowding.
Assumptions
- Up to 120 sq ft: 1 ton. Above 120 and up to 220 sq ft: 1.5 ton. Above 220 sq ft: 2 ton.
- One size up (to a maximum of 2 ton) for a sunny, top-floor or west-facing room, or more than three regular occupants.
- A ceiling of about 10 ft and a normal bedroom or living room. Kitchens, glass walls and server rooms need more.
- 1 ton of cooling = 12,000 BTU per hour = 3.517 kW. 1 square metre = 10.76 square feet.
- This is the rule of thumb brands such as Onida publish, not a heat-load calculation. An oversized AC wastes power and an undersized one runs flat out.
State tariffs differ
Electricity tariffs in India are set by each state regulatory commission, so the rate per unit, the slabs, the fixed charges and the time-of-day rules all differ by state and by electricity company. Check your own bill. These regulators publish the current orders:
- Maharashtra Electricity Regulatory Commission (MERC): electricity tariff
- Delhi Electricity Regulatory Commission (DERC): tariff orders
- Uttar Pradesh Electricity Regulatory Commission (UPERC)
If your bill has slabs, the last units you use in a month are charged at the highest rate you reach. A heavily used AC can push you into a higher slab, so use that higher rate for a better estimate.
Frequently asked questions
How many units does a 1.5 ton AC use in an hour?
It depends on the ISEER. Our formula gives about 1.17 units an hour for a 1.5 ton AC with an ISEER of 4.5 cooling at full rated capacity, and about 0.96 units at an ISEER of 5.5. Real use is usually lower once the room is cool.
Is the ISEER on the label the same as the star rating?
No. The star is a band of ISEER values. The ISEER is the actual number, so it tells you more. Star bands were revised several times, so the same ISEER can carry different stars in different years.
Why is my bill different from the calculator?
The calculator assumes full rated cooling for every hour. It also uses one flat tariff, but most state bills have slabs, fixed charges and taxes. Fans, lights and other appliances add to the same bill.
Does an inverter AC use less electricity?
Brands such as LG and Daikin say it does for long daily use, because the compressor slows down instead of switching off. The ISEER on the label already reflects this, so compare ISEER numbers.
Which tariff should I use?
Use the rate per unit on your own bill for the slab you reach in the summer months. If your usage crosses into a higher slab, use that higher rate for the extra units.
Sources
Checked on 14 October 2026. Rules and tariffs change, so confirm with the official page.