What is the formula to convert EER to SEER?

The accurate formula is: SEER = (1.12 − √(1.2544 − 0.08 × EER)) ÷ 0.04. For a quick estimate, divide EER by 0.875. This quick method works well for EER values below 14.

What is SEER2 and how is it different from SEER?

SEER2 is the updated efficiency standard introduced by the DOE in January 2023. It uses stricter testing conditions (higher external static pressure of 0.5 in H2O vs 0.1 in H2O for SEER). SEER2 ratings are typically 4.5–5% lower than SEER ratings. Convert SEER to SEER2 by multiplying by 0.955.

EER To SEER Calculator – Convert HVAC Efficiency Ratings (Free Tool)

EER to SEER Calculator: Convert HVAC Efficiency Ratings (Free Tool)

You are comparing air conditioners. One has an EER of 12. Another has a SEER of 18. Which is more efficient?

You cannot compare them directly. EER and SEER measure efficiency under different conditions. EER is a snapshot at a single high temperature. SEER is an average over an entire cooling season.

Today, I give you a free EER to SEER Calculator.

You enter an EER rating. The calculator shows the approximate SEER equivalent. It also works in reverse.

The calculator uses established conversion formulas from the California Energy Commission and industry sources .

Let me explain the difference between EER and SEER.

What is EER? (Simple Explanation)

EER stands for Energy Efficiency Ratio. It measures how efficiently an air conditioner cools when the outdoor temperature is 95°F .

The formula:

EER = Cooling Output (BTU/hr) ÷ Power Input (Watts)

Think of EER as a “stress test.” It shows how well the unit performs on the hottest day of the year.

Higher EER = More efficient at peak temperatures.

What is SEER? (Simple Explanation)

SEER stands for Seasonal Energy Efficiency Ratio. It measures efficiency over an entire cooling season, with outdoor temperatures ranging from 65°F to 104°F .

The formula:

SEER = Total Cooling Output (BTU) ÷ Total Energy Input (Watt-hours)

Think of SEER as a “marathon.” It shows average efficiency across different weather conditions.

Higher SEER = More efficient over the whole season.

Why This EER to SEER Calculator Matters

Here is why you need to convert between EER and SEER.

Reason 1: Compare units fairly

A high SEER unit may have a low EER. If you live in a hot climate, EER matters more .

Reason 2: Understand real-world performance

SEER reflects average seasonal efficiency. EER reflects peak-day performance. Both are important .

Reason 3: Energy modeling

Energy simulation software often requires EER input even when only SEER is available .

Reason 4: Utility rebates

Some programs require specific EER thresholds . The calculator helps you check.

LIVE EER to SEER Converter

Enter an EER or SEER value. The calculator finds the approximate equivalent instantly.

EER to SEER Calculator 2025 — Free HVAC Efficiency Conversion | All Formulas

EER ↔ SEER ↔ SEER2 Converter

// HVAC Efficiency Rating Calculator — DOE 2025

DOE 2025

Choose what you know

Convert from

EER Rating

10.0

Relative Efficiency Comparison

EER

SEER

SEER2

COP

Conversions use the AHRI-recommended formula: EER = −0.02×SEER² + 1.12×SEER. For EER values above 14, the simplified formula SEER ≈ EER ÷ 0.875 is used. Results are estimates — actual ratings depend on specific equipment testing conditions.

Enter your system details

SEER or SEER2 Rating

Check your AC nameplate or manual

System Size

Annual Cooling Hours

1200 hrs

Hot South: 2000–3000 · Mild North: 500–1000

Electricity Rate

$/kWh

US avg: $0.15 · CA/HI/CT: $0.25–0.40

$0/yr

Annual estimated cooling cost

Compare two systems

Current System SEER

Check old AC nameplate

New System SEER/SEER2

From new unit’s specification sheet

System Size

Annual Cooling Hours

Electricity Rate ($/kWh)

Upgrade Cost (optional)

For payback calculation

$0/yr

Annual estimated savings

Quick reference for converting between EER, SEER, SEER2, and COP. Based on AHRI standard formulas and DOE 2023 SEER2 testing methodology.

EER	SEER (approx)	SEER2 (approx)	COP	Rating

📋 SEER2 Minimums (2023+)

14 SEER2

Minimum for all split-system ACs installed after Jan 1, 2023 in most US regions. Southeast/Southwest minimum is 15 SEER2 for ≥45,000 BTU units.

⭐ Energy Star 2025

15.2 SEER2+

Energy Star certification for split-system central ACs requires 15.2 SEER2 or higher. Heat pumps require 15.2 SEER2 and 8.1 HSPF2.

2023 DOE Minimums

National (North)14 SEER2

Southeast/SW15 SEER2

Energy Star15.2 SEER2

Heat Pumps15.2 SEER2

EER2 Minimum9.8 EER2

Effective January 1, 2023. Applies to new systems manufactured after that date.

Efficiency Guide

⭐⭐⭐

20+ SEER2

Ultra high efficiency — top tier

⭐⭐

17–19 SEER2

High efficiency — good ROI

⭐

15–16 SEER2

Energy Star qualified

✓

14 SEER2

DOE minimum — meets code

⚠️

Below 14

Legacy system — consider upgrade

Quick Tips

EER is always lower than SEER for the same unit. SEER is 10–15% higher on average.

SEER2 is about 4.5–5% lower than SEER due to stricter DOE testing pressure requirements.

In hot climates (2,000+ hours/yr), upgrading from 10→18 SEER can save $400+ annually.

EER matters more for peak cooling days. SEER matters more for annual efficiency.

A proper Manual J load calculation prevents oversized units that waste energy.

What Is EER?

EER stands for Energy Efficiency Ratio. It measures how efficiently an air conditioner performs at a single specific condition. That condition is 95°F outside temperature, 80°F inside temperature, and 50% relative humidity.

EER is calculated by dividing the cooling output in BTU per hour by the electrical power input in watts. A higher EER means the unit uses less electricity to deliver the same cooling.

For example, a window AC with an EER of 10 delivers 10 BTU of cooling for every watt of electricity it uses. A unit with EER of 12 delivers 12 BTU per watt — 20% more efficient.

EER is most commonly shown on window air conditioners and portable ACs. Central AC systems usually show SEER instead. Learn more at Wikipedia: SEER ↗.

What Is SEER?

SEER stands for Seasonal Energy Efficiency Ratio. It is a more comprehensive efficiency measurement than EER. It measures performance across a whole cooling season — not just at one temperature.

SEER is calculated across outdoor temperatures ranging from 65°F to 104°F. These eight temperature ranges represent the different conditions your AC faces throughout a typical summer.

Because SEER accounts for varying conditions, it is always a higher number than EER for the same unit. The typical relationship is that SEER is about 14% higher than EER. This is why dividing EER by 0.875 gives a good SEER estimate.

The Conversion Formulas

There are two main formulas used to convert between EER and SEER. The first is more accurate. The second is a quick approximation.

Accurate Formula (AHRI Recommended)

SEER = (1.12 − √(1.2544 − 0.08 × EER)) ÷ 0.04 EER = −0.02 × SEER² + 1.12 × SEER

This formula is recommended by AHRI (Air-Conditioning, Heating, and Refrigeration Institute) for systems with EER below 14. For EER values above 14, the square root becomes impossible to calculate, so the simpler formula is used instead.

Quick Approximation Formula

SEER ≈ EER ÷ 0.875 EER ≈ SEER × 0.875

This simpler formula works well for everyday use. It is slightly less accurate than the AHRI formula but gives a good estimate for most residential AC units. Most EER values fall below 14 where both formulas give similar results.

The conversion between EER and SEER is an estimate. True SEER requires measurement at four partial load conditions (EER25%, EER50%, EER75%, EER100%). The converted value gives a good approximation but may differ from the manufacturer’s tested SEER rating.

What Is SEER2?

SEER2 is the updated efficiency standard that replaced SEER on January 1, 2023. It was introduced by the US Department of Energy to give consumers a more realistic picture of real-world efficiency.

The key difference is the external static pressure used during testing. SEER tests at 0.1 inches of water pressure. SEER2 tests at 0.5 inches. This higher pressure better simulates the actual conditions inside ductwork in a real home.

Because of this stricter test, SEER2 ratings are typically 4.5% to 5% lower than SEER ratings for the same equipment. To convert: multiply SEER by 0.955 to get SEER2.

Old SEER	SEER2 Equivalent	DOE Minimum Met?	Energy Star?
10 SEER	9.55 SEER2	No — Below Minimum	No
13 SEER	12.4 SEER2	No — Below Minimum	No
14 SEER	13.37 SEER2	No — Just Below	No
15 SEER	14.33 SEER2	Yes — Meets Minimum	No
16 SEER	15.28 SEER2	Yes	Yes
18 SEER	17.19 SEER2	Yes	Yes
20 SEER	19.1 SEER2	Yes	Yes — High Efficiency

Key things to remember about EER, SEER, and SEER2

EER measures efficiency at one fixed outdoor temperature (95°F). SEER measures it across a whole cooling season.
SEER is always higher than EER for the same unit — typically by about 14%. Divide EER by 0.875 for a quick SEER estimate.
SEER2 replaced SEER as the official standard in January 2023. SEER2 is about 4.5% lower than SEER due to stricter testing.
The national DOE minimum is 14 SEER2 for new central AC systems installed after 2023.
Energy Star certification requires 15.2 SEER2 or higher for central AC units.
COP (Coefficient of Performance) converts to EER by multiplying by 3.412. COP = EER ÷ 3.412.
Upgrading from 10 SEER to 16 SEER cuts cooling energy use by 37.5% — that is real money savings every year.

Frequently Asked Questions

How to Use This Calculator

This tool has four tabs. Each one serves a different purpose.

Convert tab — Enter any rating (EER, SEER, SEER2, or COP) and get all equivalent values instantly. Use the slider for quick browsing.
Annual Cost tab — Enter your SEER rating, system size, cooling hours, and electricity rate to see your estimated annual cooling bill.
Savings tab — Compare your old system’s SEER with a new system’s SEER. See annual savings and payback period in years.
Chart tab — Browse the full reference table showing EER, SEER, SEER2, and COP side by side for quick comparison.

For the most accurate results, use your AC unit’s actual nameplate rating. Check the yellow EnergyGuide label on your unit. For more information on SEER standards and AC efficiency, visit the Wikipedia article on SEER ↗ and the Energy Star program overview ↗.

📊 EER to SEER Converter

Convert between EER and SEER for HVAC efficiency ratings

📊 EER (Energy Efficiency Ratio)

Measured at 95°F outdoor

⇄

📊 SEER (Seasonal Energy Efficiency Ratio)

Average over cooling season

📊 EFFICIENCY METER

810121518+

💡 EER measures peak performance (95°F). SEER measures seasonal average. A unit with high SEER but low EER may struggle on hot days .

⚡ Conversion formulas based on California Energy Commission and industry sources .

EER to SEER Conversion Table

EER	SEER (approx)	Efficiency Tier
8.0	10.6	Standard
8.5	11.2	Standard
9.0	11.8	Standard
9.5	12.3	Standard
10.0	12.9	Good
10.5	13.4	Good
11.0	14.0	Good
11.5	14.5	Good
12.0	15.0	Excellent
12.5	15.4	Excellent
13.0	15.9	Premium
13.5	16.3	Premium
14.0	16.7	Premium

Based on California Energy Commission formula .

Important: For SEER2 systems, first convert SEER2 to SEER, then use the formula .

How EER and SEER Are Measured

EER (Energy Efficiency Ratio):

Measured at 95°F outdoor temperature
80°F indoor dry bulb, 67°F wet bulb
Steady-state operation
Higher EER = better performance on hot days

SEER (Seasonal Energy Efficiency Ratio):

Measured across multiple outdoor temperatures
Part-load operation included
Average over a cooling season
Higher SEER = better seasonal efficiency

The key difference: EER is a “stress test.” SEER is a “marathon.”

The Conversion Formula

The California Energy Commission provides this formula to convert SEER to EER :

EER = -0.0194 × SEER² + 1.0864 × SEER

For the calculator above, I use this formula and cap EER at 13 (as specified by the California Energy Commission) .

To go from EER to SEER, the calculator solves the quadratic equation :

SEER = (-1.0864 + √(1.0864² - 4 × (-0.0194) × EER)) ÷ (2 × (-0.0194))

Example: EER = 11

SEER = -0.0194 × 121 + 1.0864 × 11 = -2.3474 + 11.9504 = 9.6? Wait, that seems low. Let me recalculate:

Actually, the formula is for EER from SEER, not SEER from EER. The calculator solves the inverse.

For an EER of 11, the SEER is approximately 14.0.

Why EER and SEER Can Give Different Answers

Example: Two units with the same SEER (16):

Unit	EER	Performance
Unit A	12.5	Strong on hot days
Unit B	10.0	Weaker on hot days

Both have SEER 16, but Unit A performs better in hot climates .

Which to choose?

Hot climates (Arizona, Texas, Florida): Prioritize EER
Mild climates (Pacific Northwest, Northeast): SEER is more relevant

Real Examples

Example 1: EER 11

EER: 11.0
SEER: 14.0
Efficiency: Good
Best for: Hot climates, moderate cooling needs

Example 2: EER 12

EER: 12.0
SEER: 15.0
Efficiency: Excellent
Best for: Very hot climates, high cooling loads

Example 3: EER 13

EER: 13.0
SEER: 15.9
Efficiency: Premium
Best for: Commercial applications, extreme heat

Frequently Asked Questions (FAQs)

1. What is the difference between EER and SEER?

EER measures efficiency at 95°F outdoor temperature. SEER measures average efficiency over a cooling season .

2. Which is better: EER or SEER?

Neither is inherently better. EER is more important in hot climates. SEER is more relevant in moderate climates .

3. Can I convert EER to SEER?

Yes. Use the formula: SEER = (-1.0864 + √(1.0864² + 0.0776 × EER)) ÷ 0.0388 .

4. What is a good EER?

12+ is excellent. 10-12 is good. Below 10 is standard .

5. What is a good SEER?

14+ is good. 16+ is excellent. 18+ is premium .

6. Why does a unit with high SEER have low EER?

SEER includes mild temperatures where the unit runs efficiently. EER measures peak performance. Some units optimize for mild conditions .

7. What is the EER of a 16 SEER unit?

Approximately 12.0 EER (using the California Energy Commission formula) .

8. Do I need EER or SEER for a replacement?

Check your local requirements. Hot climates often require minimum EER. New equipment uses SEER2 ratings.

9. How do SEER2 and EER2 relate?

SEER2 and EER2 are the new 2023 standards. The conversion formulas are similar but use SEER2 values .

10. Where can I find EER ratings?

On the yellow EnergyGuide label or in the manufacturer’s specifications.

Common Mistakes

Mistake #1: Comparing EER and SEER directly

EER and SEER are measured differently. Do not compare them directly .

Mistake #2: Ignoring EER in hot climates

A high SEER unit with low EER may not perform well on the hottest days .

Mistake #3: Using the wrong conversion formula

Some formulas are for room air conditioners. Others are for central AC. Use the correct one .

Mistake #4: Forgetting about SEER2

New equipment uses SEER2. Convert SEER2 to SEER before using older formulas .

Final Thoughts

EER and SEER measure efficiency differently. EER is for peak performance. SEER is for seasonal average.

My EER to SEER Calculator gives you:

Quick conversion between EER and SEER
Understanding of each metric
Context for your climate

Bookmark this page. Use it when comparing air conditioners.

The next time you see EER and SEER on a label, you will know what they mean.

Disclaimer: This is an educational tool. Actual efficiency ratings depend on equipment testing. Consult your HVAC professional for specific recommendations.

External Links (Authority Backlinks):

Wikipedia – Seasonal energy efficiency ratio{:target=”_blank” rel=”noopener noreferrer”}
Wikipedia – Energy efficiency ratio{:target=”_blank” rel=”noopener noreferrer”}
California Energy Commission – HVAC Efficiency Standards{:target=”_blank” rel=”noopener noreferrer”}
ENERGY STAR – SEER/EER/HSPF{:target=”_blank” rel=”noopener noreferrer”}

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EER to SEER Calculator – Convert HVAC Efficiency Ratings (Free Tool)