Introduction
The EER Calculator shows how well your air conditioner turns power into cooling. EER stands for Energy Efficiency Ratio. It is the cooling capacity in BTU per hour divided by the power the unit pulls in watts.1 A higher EER means the unit cools more while using less electricity.
Enter your unit's cooling capacity (in BTU/h, kW, or tons) and its power input (in watts or kW). You can also add your yearly run hours and your electricity rate. The tool then gives you:
- EER: BTU/h per watt
- COP: the same efficiency shown as a plain number
- Tons of cooling: capacity in tons of refrigeration
- Annual energy use: kWh used each year
- Cost: what you pay each year and each month
You will also see each step of the math, a chart that compares your unit to federal minimum efficiency standards, and a table that ranks your EER from below average to excellent. Use it to check a nameplate rating, compare two units before you buy, or find out what your AC really costs to run.
How to use our EER Calculator
Enter your air conditioner's cooling capacity, its power use, how many hours it runs each year, and your electricity rate. The calculator gives you the EER, the COP, the size in tons, your yearly energy use, and what it costs to run.
Cooling Capacity: Type the cooling output of your unit and pick the unit of measure: BTU/h, kW, or tons. You can find this number on the nameplate or the EnergyGuide label.
Power Input: Type how much electricity the unit draws while cooling, then choose watts (W) or kilowatts (kW). This is also listed on the nameplate.
Annual Operating Hours: Type how many hours the unit runs in a year. Federal buying guidance assumes a room air conditioner runs 750 hours a year.8 For a central air conditioner it assumes 1,599 hours a year in the Southwest, 1,705 in the North and 3,409 in the hot, humid Southeast.7 The most you can enter is 8,760 hours, which is all year long.
Electricity Rate ($/kWh): Type what you pay for one kilowatt-hour of power. Check your power bill for the exact rate. In 2025, U.S. homes paid an average of about 17.30 cents per kWh, and the average for all customers was about 13.63 cents.4
Click Calculate to see your EER score, an efficiency rating, a step-by-step breakdown, and a chart that compares your unit to federal minimum efficiency standards. Click Reset to start over with the default values.
What Is EER (Energy Efficiency Ratio)?
EER stands for Energy Efficiency Ratio. It tells you how much cooling an air conditioner gives you for each watt of power it uses. A higher EER means the unit cools better while using less electricity. That means lower power bills.
The EER Formula
The math is simple:
EER = Cooling Capacity (BTU/h) ÷ Power Input (watts)
Example: an air conditioner that gives 12,000 BTU/h of cooling and pulls 1,000 watts has an EER of 12.0. Both numbers are usually printed on the unit's nameplate or its yellow EnergyGuide label.
How EER Is Tested
EER is measured at one fixed set of test conditions: 95 °F outside air, 80 °F inside air, and 67 °F indoor wet-bulb.1 In Celsius, that is 35, 26.7 and 19.4 degrees. Because the test is always the same, you can fairly compare one unit to another. This is a hot-day rating, so it shows how the unit performs when it is working hardest.
EER vs. SEER vs. COP
- EER: efficiency at one hot temperature. Best for window units, room AC, and peak-load planning.
- SEER: efficiency across a whole cooling season, with mild and hot days mixed in.1 SEER numbers are usually higher than EER for the same unit.
- COP: the same idea as EER, but with no units attached. Divide EER by 3.412 to get COP. An EER of 12 equals a COP of about 3.5, meaning the unit moves about 3.5 units of heat for every 1 unit of power it uses.
What Counts as a Good EER?
Room air conditioners made from May 26, 2026 must meet a federal minimum CEER of 12.8 to 16.0, depending on their class.2 For units of 8,000 to 13,900 Btu/h with louvered sides and no reverse cycle, the minimum is 16.0.2 Split-system central air conditioners under 45,000 Btu/h installed in the Southwest must also reach an EER2 of 11.7, or 9.8 if their SEER2 is 15.2 or higher.2 An EER under 9 is well below every current minimum.
Tons of Refrigeration
Bigger cooling systems are often sized in tons. One ton of refrigeration equals 12,000 BTU/h.3 So a 3-ton unit gives 36,000 BTU/h of cooling. This has nothing to do with weight. It comes from the old measure of how much ice it took to do the same job.
Why EER Matters for Your Bill
Your yearly cost depends on three things: how many watts the unit draws, how many hours it runs, and what you pay per kilowatt-hour. A unit with a higher EER uses fewer watts for the same cooling, so it costs less every hour it runs. The savings grow in hot climates, where an AC runs more hours. The average electricity rate for U.S. homes was about 17.30 cents per kWh in 2025.4 Your local rate may be much higher or lower, so check your utility bill.
Tips to Get Better Real-World Efficiency
- Clean or replace air filters every month during heavy use.
- Keep the outdoor coil clear of leaves, dirt, and plants.
- Seal air leaks around windows and doors so cool air stays in.
- Pick the right size unit. One that is too big cycles on and off and wastes energy.8
- Use a programmable thermostat to cut run hours.7