EER calculator
Capacity over power input, in both scales: European and US.
Your inputs
Your inputs are processed on your device and are not sent to a server.
Example loaded. You can change any value.
There is no figure yet: nothing is calculated until you ask for it.
- Enter your measurements.
- Check the units and the assumptions.
- Press Calculate, or load the example.
Rather see a worked case? Press “Load example” and change any value afterwards.
Next step
With the EER in hand, the real consumption of the unit is the next step.
Where each number comes from Conversion constants are exact; densities and coverage rates come from cited sources; everything else is an assumption you can change. Methodology · Sources and updates
How to use it
- Enter the cooling capacity in whatever unit the data sheet uses.
- Enter the electrical power input, normally in watts.
- The result gives EER in both scales: US and European.
- Use the link to estimate consumption from that EER.
How it is calculated
EER is simply what you get divided by what you spend, at one moment:
The two scales coexist and get confused constantly. A unit with an EER of 10 on the US scale has an EER of 2.93 on the European one: that is the same machine, not one three times worse.
EER is measured at a single operating point, at full load and standard test temperatures. So it does not describe an inverter unit well, since those spend most of their time at part load: that is what SEER is for.
Worked example
A 12,000 BTU/h unit drawing 1,200 W:
- US EER: 12,000 / 1,200 = 10
- Capacity in watts: 12,000 x 0.293 = 3,517 W
- European EER: 3,517 / 1,200 = 2.93
A European EER above 3.2 is considered good for a full-load figure; below 2.6, poor.
Good to know
- EER is not SEER. EER measures a point; SEER a whole season. Comparing one with the other compares different things.
- Two scales. BTU/(W·h) in the US, dimensionless (W/W) in Europe. Dividing by 3.412 converts between them.
- Test conditions. EER is measured at standard temperatures; at 40 °C outside, real performance drops.
- Capacity is not consumption. The BTU/h, frigories or kW on a label measure the heat the unit removes from the room, not the electricity it uses. For that you need the efficiency rating or the rated input power.
Frequently asked questions
What is the EER of an air conditioner?
The ratio between the cooling capacity it produces and the electrical power it draws, measured at full load. The higher it is, the less electricity it needs for the same cooling.
What is a good EER?
On the US scale, above 11 is good and below 9 is poor. On the European scale that is above 3.2 and below 2.6 respectively.
Why are there two EER values?
Because the US expresses it in BTU/h per watt and Europe as a dimensionless W/W ratio. A US EER of 10 equals a European EER of 2.93.
EER or SEER: which should I look at when buying?
SEER better describes real seasonal running costs, especially for inverter units. EER is useful for comparing performance under demanding full-load conditions.
How do I work out EER if I only have kW?
Divide the cooling capacity in kW by the power input in kW: that gives the European EER directly.