AC Power Consumption Calculator: Watts, kWh, and Running Cost
AC energy use equals input kilowatts multiplied by effective operating hours. Use measured or manufacturer input watts when possible. Then apply elapsed hours, compressor duty cycle, days, and your electricity rate to estimate kWh and cost.
Air Conditioner Power and Cost Calculator
Enter project-specific values, calculate, then change an input to compare scenarios. The result stays in this page and sends no visitor data anywhere.
EER-based input is a rated full-load estimate. Fan, standby, cycling, weather and part-load behavior can change actual bills.
Three different quantities
- Watts or kilowatts measure power at a moment.
- kWh measures energy used over time.
- Cost equals kWh multiplied by the applicable energy rate, before any demand charges, taxes, tiers, or fees not entered.
A 3,000-watt unit drawing full input for one hour uses 3 kWh. If the compressor averages a 50% duty cycle during a ten-hour window, the simplified daily compressor-equivalent use is 15 kWh. Variable-capacity equipment does not operate as a simple on/off switch, so a measured average input is better than a guessed duty cycle.
Measured watts versus an estimate
Use a manufacturer data sheet, nameplate input where it represents the operating condition, approved monitoring equipment, or a qualified measurement. Whole-system power should include the outdoor unit, indoor blower or fan, pumps, controls, and any auxiliary heat relevant to the calculation.
If watts are zero, the calculator uses cooling capacity divided by EER or EER2. For example, 36,000 BTU/h ÷ 12 EER = 3,000 watts at the rating point. This is a point estimate, not a seasonal prediction.
Why SEER and SEER2 are not instantaneous watts
SEER and SEER2 compare seasonal cooling output with seasonal electrical energy under a defined test procedure. They incorporate multiple conditions and part-load behavior. Dividing nominal BTU/h by SEER may be useful for a rough seasonal concept, but it does not reveal the unit’s actual power at a particular outdoor temperature and compressor speed. This calculator therefore asks for EER/EER2 only for its point-estimate path.
Equipment type and capacity
Central AC, heat pumps, mini-splits, and window units can have the same nominal BTU/h and different input power. Equipment type is recorded for context, but the calculation is governed by entered watts or EER. Do not assign one watts-per-ton value to every product.
Duty cycle and variable-speed systems
For single-stage equipment, duty cycle is compressor on-time divided by the elapsed window. A unit running six hours across a ten-hour period has a 60% duty cycle. The indoor fan may run longer, and crankcase heaters or standby loads can add energy.
For variable-speed equipment, use a monitored average kilowatt draw over the same window when available. A “60% duty cycle” does not mean a variable-speed compressor consumes 60% of full-rated power.
Electricity rate
Enter the marginal or blended $/kWh rate appropriate to the question. Time-of-use prices, seasonal tiers, demand charges, fuel adjustments, taxes, and fixed customer charges can make a utility bill differ from simple energy cost. Fixed charges generally do not change because the AC runs one extra hour.
Example calculation
An AC with 2,800 measured watts, a 55% duty cycle, and a 12-hour daily operating window uses about 18.48 kWh per day: 2.8 kW × 12 × 0.55. At $0.18/kWh, energy cost is about $3.33 per day and $99.79 for 30 similar days.
How this differs from “cost to run AC all day”
The existing cost-to-run-an-AC-all-day article answers that specific scenario. This page is a general-purpose calculator accepting equipment type, capacity, measured or estimated watts, hours, duty cycle, rate, and month length.
Limits and safe measurement
Weather, thermostat setting, humidity, duct condition, filter pressure drop, equipment staging, defrost, auxiliary heat, and maintenance affect real consumption. Do not open energized panels or improvise live electrical measurements. Use utility interval data, listed monitoring equipment installed as directed, manufacturer information, or a qualified professional.
Compare the estimate with the utility meter
For a whole-home system, compare similar-weather days while accounting for other large loads. Smart-meter interval data can reveal combined building demand without opening equipment. A discrepancy does not prove an AC fault by itself; water heating, cooking, vehicle charging, pool pumps, and resistance backup heat can overlap.
Cooling mode, heating mode, and auxiliary heat
For a heat pump, calculate cooling and heating operation separately. Compressor power, fan power, outdoor conditions, and capacity differ by mode. Electric auxiliary heat can add several kilowatts and should be entered from documented input or evaluated separately. A cooling-season EER estimate cannot predict a winter bill that includes resistance backup.
Power calculator FAQ
How many watts does a three-ton AC use?
There is no universal value. Use actual product input data or divide 36,000 BTU/h by the unit’s EER at the relevant rating point for a rough estimate.
Does tonnage determine monthly cost?
No. Efficiency, weather, runtime, duty, airflow, setpoint, and rate all matter.
Does one kW for one hour equal one kWh?
Yes. EIA defines a kilowatthour as one kilowatt of power used for one hour.