Energy Efficiency Ratio (EER) Calculator
Use this tool to calculate the EER of an air conditioner and estimate operating costs.
Formula: EER = Cooling Capacity (BTU/hr) ÷ Power Input (W)
What is an EER Calculator?
An EER calculator helps you measure how efficiently an air conditioner converts electricity into cooling. EER stands for Energy Efficiency Ratio, and it is one of the most practical metrics for comparing window units, portable ACs, and some central cooling systems.
In simple terms: the higher the EER, the more cooling you get for each watt of electricity. If two systems provide the same cooling, the one with the higher EER should generally cost less to run.
How EER Is Calculated
The core equation is straightforward:
EER = BTU per hour ÷ Watts
- BTU/hr = how much heat the AC removes each hour.
- Watts = how much electrical power the unit uses while running.
Example: If an AC delivers 12,000 BTU/hr and draws 1,000 watts, then its EER is 12.0.
How to Use This EER Calculator
Step 1: Enter cooling capacity
Find the unit's rated cooling output in BTU/hr from the product label or specifications sheet.
Step 2: Enter power draw
Add the power input in watts. Use rated running watts rather than startup surge values.
Step 3: Add usage assumptions
Runtime hours and local electricity price are optional but useful for estimating monthly and annual cost.
Step 4: Click Calculate
You will see the EER value, a quick efficiency rating, and estimated energy costs.
What Is a Good EER?
As a quick rule of thumb:
- 12 or higher: Excellent efficiency
- 10 to 11.9: Good efficiency
- 8.5 to 9.9: Fair efficiency
- Below 8.5: Lower efficiency
Exact standards vary by equipment type and region, but this is a useful comparison range for many residential systems.
EER vs SEER vs CEER
EER
Measured at specific test conditions (including high outdoor temperature), making it useful for hot-weather performance comparisons.
SEER
Seasonal Energy Efficiency Ratio estimates performance across an entire cooling season, not just one condition.
CEER
Combined Energy Efficiency Ratio includes standby and off-mode energy use, commonly used for room AC standards.
If you live in a very hot climate, EER often gives practical insight into peak summer electricity use.
Tips to Improve Real-World Cooling Efficiency
- Set thermostat temperatures realistically instead of overcooling.
- Seal air leaks around windows and doors.
- Clean or replace filters regularly.
- Use blinds/curtains to reduce solar heat gain.
- Keep outdoor condensers unobstructed and clean.
- Use fans to improve comfort at slightly higher thermostat settings.
Frequently Asked Questions
Does a higher EER always mean a better unit?
Usually for energy cost, yes—but also consider noise, reliability, climate suitability, sizing, and purchase price.
Can I compare different AC types using EER?
You can, but compare similar applications when possible. A well-sized unit in the right environment will perform best.
Why does my actual bill differ from calculator estimates?
Real usage varies by insulation, weather, thermostat settings, maintenance, occupancy, and utility rate structures.
Final Thoughts
This EER calculator gives you a fast way to evaluate cooling efficiency and operating cost before you buy or replace equipment. Use it alongside installation quality, system sizing, and maintenance planning to make the smartest long-term decision.