What the air conditioner costs to run
“The A/C is what drives the bill” is what everyone says, but almost nobody knows how many dollars a month that is. You can know, and two numbers are enough.
The formula, and there's only one
Watts times hours of use, divided by a thousand, gives kilowatt-hours. kWh times your real price per kWh gives dollars. That's the whole thing; the rest is detail about where each number comes from.
The price per kWh isn't the base rate published by the utility: it's what it actually costs you, and it comes from dividing your bill total by the kWh you used that period. That's the number to put in the calculator.
Where the watts come from
The label on the unit, usually on the back or the side. If it gives watts, you're done. If it gives amps and volts, multiply them and you have watts.
Careful with BTUs: they don't convert to watts by a fixed number. An efficient 12,000 BTU unit draws considerably less than an old one of the same rating, because what differs is efficiency, not cooling capacity. If BTUs are all you have, find the draw in the manual or on the nameplate before assuming anything.
It isn't running as long as you think
A conventional A/C cycles its compressor on and off to hold temperature. Even if you leave it set for eight hours, the compressor isn't running for eight, and charging yourself eight hours at full power gives a high estimate.
An inverter does the opposite: it modulates and runs nearly continuously, but at a fraction of maximum power. Its average draw usually lands below the label's nominal figure.
The fridge is the same story and it surprises people: it's never on for all twenty-four hours. So for anything that cycles, the useful estimate is effective running hours, not hours the appliance was switched on.
What to change to bring it down
Run the appliance cost calculator on every device in the house and sort them by dollars per month. The list almost always surprises: heat-producing appliances — dryer, water heater, electric stove — compete with the A/C for first place, while fans and LED bulbs barely move the needle.
With that list in front of you, the decisions get easy. A degree or two on the thermostat, closing off the room you're cooling, cleaning the filter, hanging laundry instead of drying it — each has a dollar value you can see before you change anything.
And once you have the monthly total for your appliances, compare it against your full bill in the electricity calculator. What's left over is fixed charges, and that's worth knowing too.