SEER to EER Conversion Calculator
Convert between Seasonal Energy Efficiency Ratio (SEER) and Energy Efficiency Ratio (EER) using either the quick approximate formula or the more accurate quadratic fit.
SEER
Measured over a full simulated cooling season with varying outdoor temperatures, so it reflects part-load performance and cycling efficiency.
EER
Measured at one fixed, hot outdoor condition (95°F / 35°C), so it reflects worst-case, full-load efficiency rather than a seasonal average.
Why the ratio isn't fixed
The 0.875 factor is a rough average; the true relationship is curved because higher-SEER systems gain efficiency disproportionately at part load versus full load — hence the quadratic "precise" formula.
Manufacturer data wins
Both formulas are estimates. For rebates, code compliance, or purchasing decisions, always use the EER/SEER figures on the equipment's AHRI certificate.
How to Use This Calculator
- Pick a formula — Approximate for a quick estimate, or Precise for the quadratic fit that tracks real ratings more closely.
- Choose what to solve for — EER from a known SEER, or SEER from a known EER.
- Enter the known value, or tap one of the common SEER chips (13, 14, 16, 18, 20, 21, 26) to load a typical rating.
- Read the result in the panel on the right, along with the equation used.
- Switch to Advanced mode to compare both formulas side by side and see how sensitive the result is to small changes in SEER.
What This Tool Offers
- Two formulas — a quick linear approximation and a more accurate quadratic fit, your choice.
- Two-way solving — go from SEER to EER or from EER back to SEER, including the quadratic's inverse.
- Common rating shortcuts — one-tap chips for typical residential SEER tiers.
- Step-by-step math so you can verify or show your work, not just read a final number.
- Advanced diagnostics — a side-by-side comparison of both formulas plus local sensitivity of EER to SEER.
What Are SEER and EER?
SEER (Seasonal Energy Efficiency Ratio) and EER (Energy Efficiency Ratio) both measure how much cooling an air conditioner delivers per unit of electricity, in Btu per watt-hour. SEER is a seasonal average calculated across a range of outdoor temperatures and part-load conditions, while EER is measured at a single fixed, high-load condition (95°F outdoor, per AHRI/DOE test standards). Because they're measured differently, a system's SEER and EER numbers are never identical, even though a higher rating always means better efficiency in both.
SEER to EER Conversion Formulas
Two common approximations are used to estimate one rating from the other when only one is published:
Precise: EER = −0.02×SEER² + 1.12×SEER − 0.5
The approximate formula assumes a fixed ratio between the two ratings. The precise (quadratic) formula better reflects how the SEER/EER relationship curves at higher efficiency levels, where the ratio between them tends to shift.
How to Convert SEER to EER
Select "EER" as the unknown, choose a formula, enter the SEER rating (from the equipment's spec sheet or AHRI certificate), and the calculator solves it directly. To go the other way — for example, to check what SEER a listed EER roughly implies — switch the unknown to "SEER."
| Formula | Solve for EER | Solve for SEER |
|---|---|---|
| Approximate | EER = SEER × 0.875 | SEER = EER ÷ 0.875 |
| Precise | EER = −0.02·SEER² + 1.12·SEER − 0.5 | Quadratic formula, solved for SEER |
SEER / EER Variables
| Symbol | Meaning | Typical range |
|---|---|---|
| SEER | Seasonal Energy Efficiency Ratio | 13–26+ (residential) |
| EER | Energy Efficiency Ratio at a fixed 95°F test condition | 8–17 (residential) |
Quick Reference: Common SEER-to-EER Conversions
Most residential systems fall in the SEER 13–26 range. Here's how both formulas compare across that range, along with the equivalent COP (Coefficient of Performance):
| SEER | EER (Approx.) | EER (Precise) | COP (from Precise) |
|---|---|---|---|
| 13 | 11.38 | 10.68 | 3.13 |
| 14 | 12.25 | 11.26 | 3.30 |
| 15 | 13.13 | 11.80 | 3.46 |
| 16 | 14.00 | 12.30 | 3.60 |
| 17 | 14.88 | 12.76 | 3.74 |
| 18 | 15.75 | 13.18 | 3.86 |
| 19 | 16.63 | 13.56 | 3.97 |
| 20 | 17.50 | 13.90 | 4.07 |
| 21 | 18.38 | 14.20 | 4.16 |
| 22 | 19.25 | 14.46 | 4.24 |
| 24 | 21.00 | 14.86 | 4.35 |
| 25 | 21.88 | 15.00 | 4.40 |
| 26 | 22.75 | 15.10 | 4.43 |
Below about SEER 20, the two formulas stay close; above that, they diverge more, since the Precise (quadratic) curve flattens while the Approximate formula keeps scaling linearly. The Precise formula peaks near SEER 28 — treat results at or above that point with caution, since real equipment doesn't behave that way.
SEER to EER Example
EER = 16 × 0.875
EER = 14.00
EER = −0.02×16² + 1.12×16 − 0.5
EER = −5.12 + 17.92 − 0.5
EER = 12.30
Frequently Asked Questions
SEER and EER are measured under different test conditions, so the true relationship between them depends on a specific unit's design, refrigerant, and part-load behavior. Both formulas here are estimates, not physical laws.
The quadratic "precise" formula generally tracks published ratings more closely across a wider SEER range, but for any real purchasing or compliance decision, use the manufacturer's AHRI-certified EER and SEER values instead of either estimate.
They measure different things — SEER reflects seasonal, part-load performance, while EER reflects hot-day, full-load performance. In very hot climates, EER is often given extra weight since the unit spends more time near that test condition.
COP (Coefficient of Performance) is the same efficiency concept expressed in consistent energy units instead of Btu/Wh. COP = EER ÷ 3.412, since 1 watt-hour equals about 3.412 Btu.
Variables
| Symbol | Quantity | Unit |
|---|---|---|
| SEER | Seasonal Energy Efficiency Ratio | Btu/Wh |
| EER | Energy Efficiency Ratio | Btu/Wh |
| Conversion Factor | Approximate multiplier | 0.875 (linear) or quadratic formula |
What it means
SEER and EER are both measures of air conditioner efficiency, but they are calculated under different conditions. SEER is an average over an entire cooling season, accounting for varying outdoor temperatures. EER is a single-point measurement at a high outdoor temperature (35°C). Because of this, SEER values are typically higher than EER values for the same unit. The conversion between them helps you understand how your air conditioner will perform on the hottest days of the year. This calculator gives you two conversion methods: a simple linear rule of thumb and a more accurate quadratic formula based on industry data. The linear method is quick and easy, while the quadratic method better reflects real-world performance for modern high-SEER units. Use this tool to make better comparisons and decisions for your cooling needs.
Worked example
Example 1 – Mid‑Efficiency AC (SEER 16)
Real‑World| Parameter | Value |
|---|---|
| SEER | 16.0 |
| Conversion Method | Quadratic (Precise) |
| Formula | EER = −0.02·SEER² + 1.12·SEER − 0.5 |
Example 2 – High‑Efficiency AC (SEER 22)
Premium| Parameter | Value |
|---|---|
| SEER | 22.0 |
| Linear Method | EER = 22 × 0.875 = 19.25 |
| Quadratic Method | EER = −0.02·22² + 1.12·22 − 0.5 = 15.66 |
Common mistakes
- Assuming SEER and EER are the same – they are not; SEER is always higher than EER.
- Using the wrong conversion factor – the 0.875 factor is an approximation; actual conversion depends on the specific unit and test conditions.
- Forgetting that SEER is a seasonal average, while EER is a fixed-temperature rating.
- Using the linear formula for all units – the quadratic formula is more accurate for very high SEER units.
- Not checking the manufacturer's data for the exact EER rating, which is always the most reliable.
- Confusing units – both are measured in Btu per watt-hour, but the test conditions differ.
- Applying the conversion backwards (converting EER to SEER with the same factor) – SEER ≈ EER × 1.14, not 0.875.
Applications
- Compare air conditioner efficiency ratings when shopping for a new unit.
- Estimate peak-load performance to size cooling systems properly.
- Understand how seasonal efficiency translates to real-world operation.
- Evaluate energy savings and operating costs for different AC models.
- Help HVAC technicians and engineers design efficient cooling systems.
- Convert SEER ratings from product labels to EER for technical specifications.
- Make informed decisions about upgrading or replacing existing units.
- Analyse the trade-off between seasonal efficiency and peak performance.
Related calculators · Renewable Energy & Efficiency
Recently updated formulas
Suggest an improvement
Found a mistake? Have a better example? Let us know.
You may send up to 3 suggestions per 24 hours.