EER and SEER both measure the energy efficiency of HVAC devices such as air conditioners and heat pumps.

**EER** = ‘**E**nergy **E**fficiency **R**atio’ measures energy efficiency at 100% cooling load, 50% humidity, and 95F to 80F temperature difference.

**SEER** = ‘**S**easonal **E**nergy **E**fficiency **R**atio’ measures energy efficiency throughout the summer (June, July, August). We can consider it as a real-time every EER.

Here is a universal **EER to SEER converter**. Just input the EER rating, and you’ll get the SEER rating. If you need to convert SEER to EER, you can check the SEER to EER converter here.

Inversely, if you have SEER and would like to calculate EER, you can use this SEER to EER calculator.

Here is the **EER to SEER chart** for some key EER ratings:

The formula of how to convert EER to SEER is:

SEER = (1 Ã— EER_{100%} + 42 Ã— EER_{75%} + 45 Ã— EER_{50%} + 12 Ã— EER_{250%})/100

In air conditioner specification sheets, we usually get an EER rating (many times without a SEER rating). However, the EER specified on the specs is EER_{100%}. That makes it impossible to convert from EER to SEER exactly.

Nonetheless, we can get a close estimate of what the SEER rating is from the EER ratio. For example, mini-split systems only use the SEER rating instead of the EER rating.

At EER ratings above 14, the missing measurements of EER_{25%}, EER_{50%}, EER_{75%} have a much bigger impact. Therefore any EER to SEER calculation contains a potentially larger measurement error.

Nonetheless, HVAC experts from AHRI (Air-Conditioning, Heating, and Refrigeration Institute) recommend using a simple and universal formula to calculate SEER from given EER. Here’s the formula:

**EERâ€‰= 0.875 Ã— SEER**

Using this less-accurate but more general formula, we have created a universal EER to SEER calculator (you can see it at the beginning of this article). There you can also see SEER ratings for different EER ratings in a chart.

This EER to SEER conversion is most appropriate for below 14 EER values. Most AC units fall in these categories. For example, you can check out some of the most energy-efficient AC units and see that all of them have an EER rating below 13:

- Portable AC units with 11+ EER rating here.
- Window AC units with up to 12 EER rating here.
- Ductless mini-split AC units with about 10-12 EER rating here.

## EER Below 14 (EER To SEER Calculator)

For EER up to 14, you can use a more accurate EER to SEER calculator here. Just input EER rating, and you’ll get SEER rating:

The EER to SEER calculation is based on a close approximation illustrated by the following formula:

**SEER = 1.12 -1.2544-0.08Ã—EER0.04**

Here are a few examples:

- Air conditioner with an 8 EER has a 10.68 SEER rating.
- AC unit with a 10 EER rating has a 13.86 SEER rating.
- The LG LP1419IVSM portable air conditioner with a high EER rating (EER = 10.14) has a 14.04 SEER rating.

It pays to keep in mind that these calculations of SEER are based only on EER_{100%}.

To truly calculate the SEER rating, a manufacturer has to measure EER rating at 4 different partial cooling loads, namely EER_{25%}, EER_{50%}, EER_{75%}, and EER_{100%}. Only in such a way we can calculate true SEER from EER because SEER is, in essence, a weighted average of these partial loads.