Estimate the daily, monthly, and yearly running cost of an air conditioner you already own, from its wattage or BTU capacity and efficiency.
📂 Energy & Home CalculatorsIf you know your AC's power draw in watts, enter it directly. If you only know its BTU capacity, switch the input mode, enter the BTU rating, and pick an efficiency level (or enter a custom EER) — the calculator converts that to watts automatically. Then enter your daily hours of use, days per month, and price per kWh, and press Calculate.
This tool is deliberately separate from a BTU-sizing calculator: it doesn't tell you what capacity of air conditioner to buy, only how much it costs to run one you already have. The BTU input mode uses the Energy Efficiency Ratio (EER) — the industry measure of BTU of cooling delivered per watt of electricity consumed — to convert a BTU rating into an estimated power draw in watts, since BTU alone doesn't tell you the electrical load. From there, the daily, monthly, and yearly cost follows the same watts × hours × price calculation used throughout this calculator group.
Air conditioners are usually the single largest electricity draw in homes that use them regularly, which is why even a rough running-cost estimate is worth doing before or after a purchase. A unit's nameplate wattage (if you have it) is the most direct starting point; if you only know the BTU/hr cooling capacity, the Energy Efficiency Ratio (EER) bridges the gap — a higher EER means the same cooling output for less electrical power, which is exactly why the efficiency preset matters as much as the BTU rating itself.
The comparison table (4, 8, and 12 hours of daily use) exists because actual AC runtime varies enormously by climate, room, and personal habits — someone running a unit only during the hottest afternoon hours has a very different bill than someone running it overnight for sleeping comfort. Rather than forcing a single assumption, the optional comparison lets you see the full range at a glance and plan around your actual usage pattern.
Real-world running costs can differ somewhat from this estimate because an air conditioner doesn't draw its full rated wattage every single second it's switched on — the compressor cycles off once the room reaches its target temperature and restarts when it drifts back up, similar in principle to how a refrigerator cycles. For a well-sealed, appropriately-sized room this calculator's straight-line estimate is a reasonable and commonly used approximation; a poorly insulated room or an undersized unit will run closer to continuously and cost correspondingly more.
By dividing the BTU/hr cooling capacity by the unit's EER (Energy Efficiency Ratio) — for example, a 12,000 BTU unit with an EER of 10 draws roughly 1,200 watts. A higher EER means the same cooling for less electricity.
It's usually printed on the unit's nameplate or energy label, often alongside the BTU rating. If you can't find it, the standard/high-efficiency/inverter presets in this tool give a reasonable range to choose from.
The BTU Calculator (under Construction & Home Improvement) helps you size a new air conditioner for a room you don't yet have one in. This tool assumes you already own a specific unit and estimates what it costs to run.