Estimate how much your air conditioner costs to run using BTU and efficiency or a listed watt number.
Table of contents
How to use our Air Conditioner Running Cost Calculator
- Choose What number do you know?: use BTU and efficiency for cooling size plus SEER, EER, CEER, SEER2, or EER2, or use Watts when you have running watts.
- Enter Time AC is on (hours per day) and Electricity rate ($ per kWh) from your bill or a realistic local rate.
- Open Advanced options if you want to change Days used, lower Average cooling effort, or add Extra bill add-ons.
- Click Calculate and read Estimated cost for the selected days first, then check kWh and cost per day for context.
- Sanity-check the result: if the watts seem much higher than a normal running label, make sure you did not enter startup watts, breaker amps, or locked-rotor amps.
Definitions
BTU per hour: A cooling size rating. Higher BTU per hour means the AC can move more heat out of the room or home.
Efficiency rating: SEER, EER, CEER, SEER2, or EER2 tells how many BTUs of cooling the AC delivers for each watt-hour of electricity. Higher is more efficient.
Power draw (watts): The running electrical power used while the AC is cooling. This is not startup watts.
kWh: Kilowatt-hour, the energy unit on most electric bills. A 1000 watt device running for 1 hour uses 1 kWh.
Average cooling effort: The percent of entered on-time treated as full-power cooling time. At 50%, 8 hours on counts like 4 full-power hours.
Extra bill add-ons: Extra percent added to energy cost for per-kWh charges not already included in your electricity rate.
Tons of cooling: A common AC size unit. One ton of cooling equals 12000 BTU per hour.
Common mistakes and quick fixes
Mistake: Entering startup watts in Power draw (watts).
Fix: Use running watts from the label, spec sheet, or plug-in meter.
Mistake: Using Power draw (watts) while What number do you know? is set to BTU and efficiency.
Fix: Switch What number do you know? to Watts so the calculator uses the watt number directly.
Mistake: Treating Time AC is on (hours per day) as only the hours the compressor runs.
Fix: Enter the hours the AC is turned on, then adjust Average cooling effort if it cycles off part of the time.
Mistake: Entering a base supply price in Electricity rate ($ per kWh) and also adding the same delivery charges in Extra bill add-ons.
Fix: If your rate already includes delivery, taxes, and fees, keep Extra bill add-ons at 0.
Mistake: Leaving Days used at 30 when you want a whole summer estimate.
Fix: Change Days used to the number of cooling days you want, such as 90.
Limitations & Key Assumptions / Boundary Conditions
- The estimate is a bill estimate, not a live meter reading. Weather, thermostat setting, insulation, sunlight, duct losses, filter condition, and equipment age can change real use.
- BTU and efficiency mode estimates full-power draw by dividing Cooling size (BTU per hour) by Efficiency rating. Seasonal ratings such as SEER or SEER2 may not match one hot afternoon.
- Watts mode is usually safer when you have a real running Power draw (watts) from a nameplate, spec sheet, or plug-in meter.
- Average cooling effort is a simple percent. It does not model variable-speed compressors, fan-only time, humidity removal, defrost cycles, or standby power.
- Electricity rate ($ per kWh) must match your bill goal. If you enter an all-in delivered rate, do not also add the same charges in Extra bill add-ons.
- The calculator does not show annual cost unless you enter 365 in Days used, because many air conditioners do not run all year.
Methodology
How the calculator chooses power
If you choose BTU and efficiency, the calculator estimates full-power watts from cooling size and the efficiency rating. EER is often used for room air conditioners, while SEER is often used for central air conditioners [2].
power_watts = cooling_capacity_btu_per_hr / efficiency_rating
If you choose Watts, the calculator uses the entered running Power draw (watts) directly.
power_watts = rated_power_watts
How energy and cost are calculated
Average cooling effort turns scheduled on-time into full-power-equivalent hours.
active_hours_per_day = hours_per_day * cycle_percent / 100
energy_per_day_kwh = power_watts / 1000 * active_hours_per_day
energy_per_period_kwh = energy_per_day_kwh * days_used
estimated_period_cost = energy_per_period_kwh * electricity_rate_per_kwh * (1 + extra_bill_addons_percent / 100)
cost_per_day = estimated_period_cost / days_used, or 0 when days_used is 0
cost_per_scheduled_hour = power_watts / 1000 * electricity_rate_per_kwh * (cycle_percent / 100) * (1 + extra_bill_addons_percent / 100)
For BTU and efficiency mode, the displayed size in tons is calculated as:
entered_size_tons = cooling_capacity_btu_per_hr / 12000
Mini-example
A 12000 BTU per hour AC with an efficiency rating of 12 has an estimated full-power draw of 1000 watts. If it runs 8 hours per day for 30 days at $0.18 per kWh with 100% cooling effort, it uses 240 kWh and costs $43.20 for the selected days.
Calculation choices
Commas and spaces are removed before numbers are parsed. Hidden mode-specific inputs are not used. If Days used is 0, cost per day is shown as $0 to avoid dividing by zero.