With the July heat, the air conditioner stays on for hours, and the bill becomes a constant worry. But how much does it really cost to run it? Many people ask themselves this question, often with a little anxiety, and the answer is simpler than it seems: all it takes is three numbers and a multiplication.
In this guide, we will look at how much electricity an air conditioner consumes in kWh, how to translate that consumption into euros on your bill, and what increases (or decreases) the cost. With real numbers, updated to 2026, and a table for the most common sizes, so you can calculate it for your own home.
You might also be interested in: “Energy saving with air conditioning: 10 practical tips”
What determines air conditioner consumption
Before we get to the numbers, we need to understand what determines them. Two air conditioners with identical power can consume very different amounts of energy, and the reason lies in a handful of factors.
The first is BTU power: the higher it is, the more energy is needed to run it. An 18,000 BTU unit consumes more than a 9,000 BTU unit, that's inevitable. The second is the energy class: for the same BTU, an A+++ class model can consume up to 40% less than a lower class one. The third is inverter technology, which, by modulating the power, saves 30-40% compared to older on/off models. Then there are the usage factors: how many hours you keep it on, at what temperature, how insulated the room is, and how hot it is outside.
All of this explains why there isn't a single answer to the question "how much does it consume?". However, there is a precise way to calculate it in your specific case.
The formula for calculating consumption
The calculation is simple and is based on three data points:
Power consumption (kW) × hours of use × cost per kWh (€) = expense
You can find the power consumption on the energy label or the technical sheet of the air conditioner, expressed in watts (W) or kilowatts (kW). Be careful not to confuse it with BTUs: BTUs indicate cooling power, watts indicate how much electricity the machine draws to produce it.
You can find the cost per kWh on your bill. As a reference, in 2026, the average "all-inclusive" price for an Italian family, including energy, transport, charges, and taxes, will be around €0.25/kWh. This is the value we will use here for calculations, but if you want the precise data, check your bill.
Let's take a concrete example. An air conditioner that draws 1 kW, kept on for 8 hours a day, consumes 8 kWh per day. Multiplying by €0.25, that's 2 euros per day. Over a month of use, about 60 euros. That's all there is to the mechanism.
How much does a 12,000 BTU air conditioner consume?
Let's start with the best-selling size, the one installed in most Italian homes: the 12,000 BTU, suitable for living rooms and rooms up to approximately 35-40 square meters.
A 12,000 BTU inverter in class A+++ consumes on average about 0.8-1 kWh per hour. In lower class models, it easily goes up to 1.2 kWh. Taking the average value of 1 kWh and the usual 8 hours a day, the calculation is quickly done: about 2 euros per day, around 60 euros per month of intense use.
But here's the interesting data: over the entire summer season, calculated on actual operating hours (the inverter modulates, it doesn't always run at maximum), a 12,000 BTU unit in class A+++ consumes about 140 kWh per year, equivalent to just over 35 euros per season. The same model in class A consumes 200-220, reaching 50-55 euros. The difference is made by efficiency, not just the hours.
Consumption and cost table by size
Here's an overview for the three most common sizes, considering efficient inverter models, 8 hours of daily use, and a cost of €0.25/kWh. These are indicative values: actual consumption depends on insulation, set temperature, and external climate.
|
Power |
Hourly Consumption |
Cost per Day (8h) |
Cost per Month |
|
9,000 BTU |
~0.7-0.8 kWh |
~€1.50 |
~€45 |
|
12,000 BTU |
~0.8-1 kWh |
~€2.00 |
~€60 |
|
18,000 BTU |
~1-1.3 kWh |
~€2.60 |
~€78 |
A couple of useful clarifications. These amounts are calculated on average continuous consumption: in reality, a well-sized inverter in an insulated home consumes less, because once the temperature is reached, it slows down and consumes little. And if you are on a free market offer with a lower kWh price, the costs will decrease accordingly.
How much does it cost to keep it on all day?
It's one of the most frequently asked questions: what if I leave it on for 24 hours? Let's look at the numbers, because they are less frightening than you might think.
A good-class 9,000 BTU inverter, running continuously, actually consumes around 9-10 kWh per day, not the full 24 hours of maximum absorption, because after the initial phase it modulates to a minimum. That's about 2.30-2.50 euros per day. A 12,000 BTU in the same conditions reaches 12-13 kWh, around 3 euros per day.
The important point is precisely this: the actual consumption is much lower than the theoretical calculation that multiplies the maximum power by 24. An inverter works hard only at the beginning, to bring the room to temperature; then it merely maintains it, absorbing a fraction of the power. This is why, if you are constantly in and out, it is often better to leave it at a constant temperature rather than turning it off and on again, but this is a matter of good habits, which we have explored elsewhere.
How much does energy class affect the bill?
If there's one factor that makes a difference in consumption, for the same power, it's the energy class. And the difference isn't theoretical: it's money.
For a 12,000 BTU unit, the difference between an A+++ class and an A class is around 30-35 euros per season. Said like that, it might seem like a small amount. But an air conditioner lasts an average of ten years: that's 300-350 euros over its lifetime, often more than the surcharge you pay for a top-of-the-range model at the time of purchase. That's why choosing a high class is not a luxury, but an investment that pays for itself.
The two indices found on the technical data sheet also count for a lot: the SEER, which measures cooling efficiency, and the SCOP, which measures heating efficiency. The higher they are, the less the machine consumes for the same performance. A model with a SEER greater than 8.5 is at the top of the A+++ class and guarantees the lowest possible consumption.
How to spend less, in summary
Putting together what we've seen, your air conditioning bill depends on three levers you can truly influence:
- The right machine: an inverter model in a high energy class, correctly sized in BTUs for your room. An oversized or undersized air conditioner always consumes more than it should. If you have doubts about the size, start with the BTU guide for each room.
- Smart usage: temperature around 24-26 °C, filter maintenance, scheduling of operating hours. Small habits that, combined, are worth tens of euros per season.
You don't need to give up coolness to spend less. You just need to choose well and use the machine with a minimum of common sense.
And if your air conditioner is a few years old and in a low energy class, the best way to spend less is to replace it with an efficient model: you'll notice the difference in your bill from the very first summer. On Worldclima, you'll find a selection of high-efficiency air conditioners, with complete technical data sheets to compare consumption, classes, and SEER values. Choose the most efficient one.
To learn more: “How to choose an air conditioner: complete guide to avoid mistakes”