AC Energy Cost Calculator
Calculate how much your air conditioner costs to run per day, month, and year. Enter your AC unit's BTU rating, energy efficiency (EER/SEER), daily usage hours, and local electricity rate to get an accurate cost breakdown.
How the AC Energy Cost Calculator Works
An AC energy cost calculator estimates how much electricity your air conditioning unit consumes and what that costs you in real dollars. Air conditioners are rated by BTU (British Thermal Units), which measures cooling capacity, and by EER or SEER, which measures energy efficiency. This calculator converts your AC's BTU rating into wattage using the efficiency rating, then multiplies by your daily usage hours and electricity rate to produce daily, monthly, and annual cost estimates. Based on U.S. Energy Information Administration 2025 data, the average American household spends approximately $265 to $525 per year on air conditioning, depending on climate zone and unit efficiency.
AC Energy Cost Formulas
Wattage = BTU Rating ÷ EER
Daily kWh = Wattage × Hours Per Day ÷ 1,000
Monthly kWh = Daily kWh × 30
Monthly Cost = Monthly kWh × Rate Per kWh
Annual Cost = Monthly Cost × Months of Use
Where:
- BTU Rating = The cooling capacity of your AC unit (higher BTU = more cooling power)
- EER (Energy Efficiency Ratio) = BTU output per watt of electricity consumed (higher = more efficient)
- Hours Per Day = How many hours the AC runs each day on average
- Rate Per kWh = Your local electricity price per kilowatt-hour
Choosing the Right AC Size for Your Room
Selecting the correct BTU rating for your space is critical for both comfort and energy efficiency. An undersized unit runs constantly without adequately cooling the room, wasting electricity. An oversized unit cycles on and off too frequently, which increases wear, reduces dehumidification, and raises energy costs. As a general guideline from the U.S. Department of Energy, a 150-square-foot room needs approximately 5,000 BTU, a 350-square-foot room needs 8,000 BTU, a 550-square-foot room needs 12,000 BTU, and areas over 1,000 square feet require 18,000 to 24,000 BTU or a central air system. Factors like ceiling height, sun exposure, insulation quality, and the number of occupants can shift these requirements by 10% to 30%.
Understanding EER and SEER Ratings
EER (Energy Efficiency Ratio) measures an air conditioner's efficiency at a single outdoor temperature (typically 95 degrees Fahrenheit), while SEER (Seasonal Energy Efficiency Ratio) measures average efficiency across an entire cooling season with varying temperatures. SEER ratings are always higher than EER for the same unit because they include milder conditions. A modern Energy Star-certified window unit typically has an EER of 12 or higher, while central air systems are rated by SEER with minimum standards of 14 to 15 SEER depending on region. Upgrading from an older 8 EER unit to a modern 12 EER unit reduces electricity consumption by 33%, which translates directly into lower monthly bills. When comparing units, always use the same rating type — comparing an EER of 10 to a SEER of 16 is misleading because they measure different conditions.
Tips to Reduce AC Running Costs
Several practical steps can significantly lower your air conditioning expenses. Set your thermostat to 78 degrees Fahrenheit when home and higher when away — each degree lower increases energy use by 3% to 5%. Use ceiling fans to create a wind-chill effect that lets you raise the thermostat by 4 degrees without losing comfort. Clean or replace AC filters monthly during heavy use, as dirty filters force the unit to work 5% to 15% harder. Seal air leaks around windows and doors, close blinds on sun-facing windows during peak heat, and ensure your ductwork is properly insulated. Consider a programmable or smart thermostat that automatically adjusts temperatures based on your schedule. Running your AC during off-peak electricity hours can also save money if your utility offers time-of-use pricing.
SEER vs SEER2: Which Number Should You Enter in 2026?
If your AC was bought in the last few years, the sticker probably says SEER2, not SEER — and entering one where the other belongs will skew your running cost. Since 1 January 2023 the US Department of Energy has rated central and mini-split systems using SEER2, EER2 and HSPF2. The rating itself did not get worse; the test got harder. The new Appendix M1 procedure raises the external static pressure used in testing by up to five times, so the rating reflects the duct resistance a system actually meets in a house rather than on a lab bench.
The practical effect is that a SEER2 figure runs roughly 4.5% lower than the SEER figure for the same physical equipment. A unit previously advertised at 16 SEER is about 15.2 SEER2. So when you compare a 2019 quote against a 2026 quote, you are not looking at a downgrade — you are looking at two different yardsticks. For this calculator, enter whichever number is on your unit and treat it as an efficiency ratio; just do not mix a SEER2 value for one quote with a SEER value for another, because the newer standard will look artificially worse.
One more distinction worth keeping straight: EER measures a single hot-day operating point, SEER and SEER2 average a whole cooling season. Window and portable units are still commonly rated by EER (or CEER), which is why the EER of 12 used in the comparison above is not directly comparable to a 15 SEER2 central system. If you want a like-for-like monthly cost, run the calculator once per unit using each unit's own rating type rather than converting between them. Sources: US Department of Energy — 2023 central air conditioner standards FAQ, AHRI — 2023 energy efficiency standards and EIA Electric Power Monthly, Table 5.6.A. Last updated: August 2026.
AC Cost Comparison by Unit Size
These estimates assume 8 hours per day of use, an EER of 12 (a typical efficient unit) and the current US residential average electricity price of 18.44 cents per kWh (EIA, May 2026). A 5,000 BTU window unit draws 417 watts and costs about $18 per month, suitable for a small bedroom. A 12,000 BTU unit for a living room draws 1,000 watts and runs about $44 per month. A 24,000 BTU unit or mini-split for a large open area draws 2,000 watts and costs around $89 per month. Note that these are noticeably higher than the figures you will see on older calculators still using a 15 or 16 cent rate — residential electricity prices rose 6.2% year on year to May 2026. These estimates assume consistent daily usage — actual costs depend on your thermostat settings, outdoor temperature, insulation, and whether the unit cycles on and off rather than running continuously. Use the calculator above with your specific numbers for a personalized estimate.
Frequently Asked Questions
How much does it cost to run an air conditioner per hour?
The hourly cost depends on your AC's wattage and your electricity rate. A typical 12,000 BTU window unit with an EER of 12 draws 1,000 watts (1 kW). At the US residential average of $0.1844 per kWh (EIA, May 2026), that costs about $0.18 per hour. A less efficient 8 EER unit of the same size draws 1,500 watts and costs about $0.28 per hour — 50% more. Central air systems with higher BTU ratings cost proportionally more per hour but may cool your entire home more efficiently than multiple window units.
What is the difference between EER and SEER ratings?
EER (Energy Efficiency Ratio) measures efficiency at a single test condition — typically 95°F outdoor temperature. SEER (Seasonal Energy Efficiency Ratio) averages efficiency across an entire cooling season with temperatures ranging from 65°F to 104°F. SEER ratings are always higher than EER for the same unit because they include milder conditions where the AC works less hard. Window and portable units are typically rated by EER, while central air and mini-split systems use SEER. For this calculator, you can use either rating — just be consistent when comparing units.
How many BTU do I need for my room size?
The U.S. Department of Energy recommends approximately 20 BTU per square foot of living space as a baseline. A 150 sq ft bedroom needs about 5,000 BTU, a 300 sq ft room needs 8,000 BTU, a 450 sq ft room needs 10,000-12,000 BTU, and spaces over 700 sq ft need 15,000-18,000 BTU or more. Adjust upward by 10% for sunny rooms, add 600 BTU per additional person beyond two occupants, and add 4,000 BTU if the unit is in a kitchen. Oversizing wastes energy through short-cycling, while undersizing causes the unit to run constantly.
Does running AC at a higher temperature save money?
Yes, raising your thermostat setting significantly reduces AC costs. The Department of Energy estimates that each degree you raise the thermostat above 72°F saves 3% to 5% on cooling costs. Setting your AC to 78°F instead of 72°F can save approximately 18% to 30% on your cooling bill. Using a ceiling fan in conjunction with a higher thermostat setting creates a wind-chill effect that makes 78°F feel like 72°F while using far less energy than lowering the AC temperature.
Is it cheaper to run AC all day or turn it on and off?
It is generally cheaper to use a programmable thermostat that raises the temperature when you are away and cools the home before you return. Turning AC completely off and then cooling a hot house uses a burst of energy, but it is still typically less total energy than running AC all day in an empty home. The most efficient approach is to raise the thermostat by 7-10°F for 8 hours while you are at work — the DOE estimates this saves up to 10% annually on cooling costs. Smart thermostats automate this process and learn your schedule for optimal savings.
How much electricity does a window AC use compared to central air?
A typical window AC unit (8,000-12,000 BTU) uses 700 to 1,200 watts, while a central air conditioning system (24,000-60,000 BTU) uses 3,000 to 5,000 watts. However, central air cools the entire home, so the cost per square foot of cooled space may be similar or even lower than running multiple window units. If you only need to cool one or two rooms, window units are more economical. If you need whole-home cooling, a modern central system with a SEER rating of 16 or higher is typically the most cost-effective option.
What is the average electricity rate to use in this calculator?
The US residential average is 18.44 cents per kWh as of May 2026, according to EIA Electric Power Monthly Table 5.6.A — up 6.2% year on year. That is the default this calculator uses. Your own rate can differ a lot by state, so check the "price per kWh" line on your utility bill: rates run from roughly 11 cents in some southern and midwestern states to over 30 cents in Hawaii, California and parts of New England. Because monthly cost scales linearly with the rate, using your actual tariff is the single biggest accuracy improvement you can make.
What is the difference between SEER and SEER2?
SEER2 replaced SEER as the US efficiency rating for central and mini-split air conditioners on 1 January 2023. The equipment did not change — the test did. The Appendix M1 test raises the external static pressure by up to five times so the rating reflects the duct resistance a system meets in a real house. As a result a SEER2 number is about 4.5% lower than the SEER number for the same unit: a system once sold as 16 SEER rates roughly 15.2 SEER2. When comparing an older quote with a new one, make sure both use the same yardstick or the newer system will look worse than it is.