Enter the total electric energy output for a given period of time and the maximum possible output over the same time to determine the capacity factor.

Capacity Factor Formula

The following formula is used to calculate a capacity factor.

  • Where CF is the capacity factor
  • AEO is the actual electrical output over a time period
  • MEO is the maximum electrical output over time

To calculate a capacity factor, divide the actual output by the maximum output.

Capacity Factor Definition

A capacity factor is a ratio of the actual electrical output of an electricity-producing installation or facility over the maximum amount of electricity the facility could theoretically produce.

In other words, the capacity factor is a measure of an installation’s uptime over a given period.

Example Problem

How to calculate a capacity factor?

  1. First, determine the total possible electrical output over a time period.

    For this example, we are looking at a nuclear power plant that generates electricity. Over a period of a month the total possible electrical output is found as 30 days * 24hrs/day * 3500 MW = 2,520,000 MW.

  2. Next, determine the actual electrical output of the plant over the same month.

    Using data from the plant itself, the electrical output is found to be 2,000,000 MW over the past month.

  3. Finally, using the formula CF = AEO / MEO, calculate the capacity factor.

    The capacity factor is found to be: 2,000,000/2,520,000 = .7936.


What is a good capacity factor?

In general, a capacity factor should be as close to 1, or 100%, as possible. This means that the plant is running at full capacity 24/7 and that generates revenue for the plant. The current grid system is designed so that most plants supply close to their maximum output constantly, then “peaker” plants supply extra electricity to handle spikes in demand.

Is capacity factor a percentage?

A capacity factor is most often displayed as a unitless ratio, but sometimes the ratio and the percentage are used interchangeably.

What is the capacity factor of solar plants?

The capacity factor of solar plants depends on the location of the plant itself. Plants closer to the equator will have longer amounts of time with the sun and will run at a higher capacity. At most, solar plants run between .3 and .4 for a capacity factor. This is because although there could be days with more than 12 hours of sun, the sun does not directly hit the solar panels the entire day so the maximum output is reduced.