EER Calculator

Quick answer

The energy efficiency ratio is EER = cooling capacity (BTU/h) ÷ power input (watts), and COP = EER × 0.2930710702. An air conditioner of 12,000 BTU/h using 1,000 W has an EER of 12 and a COP of 3.517.

Enter the cooling capacity in BTU/h and the power input in watts. The calculator returns EER and COP.

Related tools: Specific Heat Calculator: Specific heat capacity or heat required from Q = m c ΔT. Thermodynamic Processes Calculator: Work, heat and internal energy for an ideal gas process. Heat Pump COP Calculator: Coefficient of performance from heat output and power input, or the Carnot limit.

How to use the EER Calculator

1. Enter cooling capacity (BTU/h) (above 0).
2. Enter power input (W) (above 0).
3. Press Calculate to see the result, and use Reset to start again.

Formula and method

1 BTU/h = 0.2930710702 W.

Worked examples

These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.

The first line is the headline result (eER). Below it the eER Calculator lists cOP, which describe the same case from other angles. IEEE-754 double precision; shown to the decimals indicated.

Reading EER

A higher EER means more cooling per watt. Room air conditioners typically range from about 9 to 12; central units use SEER, a seasonal average. COP is the dimensionless version: 3.5 units of heat moved per unit of electricity.

Rated values

Use the rated, not measured, capacity and power from the nameplate. At the same capacity, an EER of 12 uses 1,000 W against 1,200 W for an EER of 10: a 17% saving.

How the result changes with cooling capacity

Holding every other input at the first worked example, this table changes only cooling capacity. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.

What happens with invalid input

These messages are produced by the calculator itself, so you know what to fix.

• Cooling capacity: entering "0" shows "Cooling capacity must be greater than 0." beside that field and no result.
• Power input: entering "0" shows "Power input must be greater than 0." beside that field and no result.

Choosing between the EER Calculator and similar calculators

Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.

Background: heat and temperature

The basic heat relation is Q = m × c × ΔT: heat in joules equals mass times specific heat capacity times temperature change. A positive Q means heat absorbed and a negative Q heat released, and a change in °C is numerically the same as a change in K.

It covers a change in temperature only. During melting or boiling the temperature stays constant while heat still flows (latent heat), which needs a separate term.

Assumptions and limitations

• Use rated, not measured, capacity

If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for cooling capacity and power input to confirm this.

Related calculators

• Specific Heat Calculator — Specific heat capacity or heat required from Q = m c ΔT.
• Thermodynamic Processes Calculator — Work, heat and internal energy for an ideal gas process.
• Heat Pump COP Calculator — Coefficient of performance from heat output and power input, or the Carnot limit.
• Heat Transfer Calculator — Conductive heat flow through a flat wall.
• Thermal Expansion Calculator — Change in length from a temperature change.
• Electron Configuration Calculator — Ground-state electron configuration of an element or monatomic ion, with noble-gas shorthand and unpaired electrons.

Sources

• NIST SP 811 BTU(IT) conversion

Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.