Enter the apparent power (watts) and the reactive power (watts) into the calculator to determine the Active Power. 

Active Power Formula

The following formula is used to calculate the Active Power. 

Pa = SQRT ( AP^2 – RP^2)

  • Where Pa is the Active Power (watts)
  • AP is the apparent power (watts) 
  • RP is the reactive power (watts) 

How to Calculate Active Power?

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

Example Problem #1:

  1. First, determine the apparent power (watts). In this example, the apparent power (watts) is measured to be 40.
  2. Next, determine the reactive power (watts). For this problem, the reactive power (watts) is calculated to be 20.
  3. Finally, calculate the Active Power using the formula above: 

Pa = SQRT ( AP^2 – RP^2)

Inserting the values from above and solving the equation with the imputed values gives: 

Pa = SQRT (40^2 – 20^2) = 34.64 (watts)


Example Problem #2: 

Using the same process as example problem 1, we first define the variables outlined by the formula. In this case, the values are:

apparent power (watts) = 70

reactive power (watts) = 20

Entering these values into the formula or calculator above gives us: Pa = SQRT ( 70^2 – 20^2) = 67.08 (watts)