Calculate power supply efficiency from input and output power, or estimate heat loss, yearly energy use, and cost from load and efficiency.

Use real input and output power measured at the same load. Efficiency changes with load and operating conditions.

Power Supply Efficiency Formula

The following formula is used to calculate the Power Supply Efficiency. 

Eps = (OP / IP) ร— 100
  • Where Eps is the Power Supply Efficiency (%)
  • OP is the unit output power (watts) 
  • IP is the supply input power (watts) 

To calculate the power supply efficiency, divide the unit output power by the supply input power, then multiply by 100 to express it as a percentage. In real power supplies, the efficiency is typically less than 100%.

How to Calculate Power Supply Efficiency?

The following two example problems outline how to calculate the Power Supply Efficiency.

Example Problem #1:

  1. First, determine the supply input power (watts). In this example, the supply input power (watts) is given as 100.
  2. Next, determine the unit output power (watts). For this problem, the unit output power (watts) is given as 60.
  3. Finally, calculate the Power Supply Efficiency using the equation above: 

Eps = (OP / IP) * 100

Inserting the values from above and solving the equation: 

Eps = 60 / 100 * 100 = 60 (%)

Example Problem #2: 

Using the same process as above, first define the variables required by the formula. In this case, these values are:

supply input power (watts) = 200

unit output power (watts) = 50

Entering these values yields:

Eps = 50 / 200 * 100 = 25 (%)