AC Running Cost Calculator
How the formula works
The calculator finds the electrical power of the AC, estimates the average power while running, and multiplies the energy by your electricity price.
Formulas
Rated power (kW) = Capacity (TR) × 12,000 / EER / 1000
Or, from nameplate: Rated power (kW) = Input watts / 1000
Average power = Rated power × Average load %
Energy per day (kWh) = Average power × Hours per day × Number of ACs
Energy per month = Energy per day × Days per month
Cost = Energy × Price per kWh × (1 + Extra charges %)
Where:
- 1 TR = 12,000 BTU/h
- EER = cooling output in BTU/h divided by electrical input in watts
- One kWh is also called one unit of electricity
Typical values
EER: 9 for old or basic ACs, 11 to 12 for good models, 13 to 14 for high efficiency models. Average load: inverter AC about 60 % of rated power, fixed speed AC about 80 %. These are typical planning values. Real use depends on the room, the weather and the thermostat setting, so use the Custom option for your own figures. The nameplate on your AC and your electricity bill are the best sources.
How to use the calculator: choose how you know the AC power, enter the AC details, running hours, days and electricity price, then click Calculate.
Important notes: some tariffs use slabs, time-of-day rates or fixed charges. This calculator uses one flat price per unit.
Worked example
Example 1: 1.5 TR inverter AC
EER 11, inverter (60 %), 8 hours per day, 30 days, price 8 per kWh.
Rated power = 18,000 / 11 / 1000 = 1.64 kW. Average power = 0.98 kW. Energy per day = 7.85 kWh. Per month = 235.6 units. Cost per day = 62.84. Cost per month = 1,885.09.
Example 2: Three 1,500 W fixed speed ACs
Nameplate 1,500 W, fixed speed (80 %), 10 hours per day, 26 days, price 0.15 per kWh, 5 % extra charges.
Average power = 1.20 kW. Energy per day = 1.2 × 10 × 3 = 36.00 kWh. Per month = 936 units. Cost per month = 936 × 0.15 × 1.05 = 147.42.
Example 3: 2 TR AC, seasonal use
EER 12, fixed speed (80 %), 12 hours per day, 30 days, price 7.5 per kWh, 6 months per year.
Rated power = 2.00 kW. Average power = 1.60 kW. Energy per day = 19.20 kWh. Per month = 576 units. Cost per month = 4,320.00. Cost for 6 months = 25,920.00.
Example 4: Two 1 TR ACs at full power
EER 9.5, full power (100 %), 6 hours per day, 22 days, price 10 per kWh.
Rated power = 1.26 kW each. Energy per day = 15.16 kWh. Per month = 333.5 units. Cost per month = 3,334.74.
Common mistakes
- Using the cooling capacity (TR or BTU/h) as if it were electrical power.
- Forgetting that the AC does not draw full power all the time.
- Counting the hours the room is occupied instead of the hours the AC actually runs.
- Using the price per unit from an old bill or the wrong slab.
- Ignoring fixed charges, taxes and fuel surcharges.
- Comparing a fixed speed AC and an inverter AC without allowing for their different average loads.
- Forgetting that a very low thermostat setting increases the running time.
- Counting the full year when the AC is used only for a few months.
- Using the wrong EER for an old AC with a dirty filter or low gas.
Frequently asked questions
How much electricity does a 1.5 TR AC use?
A 1.5 TR AC with EER 11 draws about 1.64 kW at full power and about 1 kW on average for an inverter AC.
How do I calculate AC electricity cost per month?
Multiply the average kW by the hours per day and the days per month, then multiply by the price per unit.
What is one unit of electricity?
One unit is one kilowatt-hour (kWh), which is a 1 kW load running for one hour.
What is EER?
EER is the cooling output in BTU/h divided by the electrical input in watts. A higher EER means lower running cost.
Is an inverter AC cheaper to run?
Usually yes. It adjusts its speed to the load, so the average power is lower than a fixed speed AC.
Where do I find my AC power in watts?
Look at the nameplate or the data sheet for the rated input power in watts.
What is the average load percentage?
It is the share of rated power the AC draws on average while running. It changes with the room, the weather and the thermostat setting.
How can I reduce my AC bill?
Set the thermostat to 24 to 26 °C, clean the filters, seal the room, use blinds and choose an inverter or high EER model.
Does a bigger AC cost more to run?
A bigger AC draws more power but may run for fewer hours. An oversized AC also cycles often and wastes energy.
How do I find the right AC size?
Use the AC Tonnage Calculator first, then enter the size here to see the running cost.
Can I calculate the cost for several ACs?
Yes. Enter the number of ACs and the cost is multiplied.
Is this the exact cost on my bill?
No. It is an estimate based on one flat price per unit. Slabs, time-of-use rates and fixed charges can change the bill.