Enter any three values (voltage, real power, power factor, and/or current) and select single-phase or three-phase to calculate the missing AC current-related value.

AC Current Calculator

Enter any 3 values to calculate the missing one. Use RMS voltage; for three-phase, enter line-to-line (L-L) RMS voltage.

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AC Current Formula

The following formulas are used to calculate AC current from real power, voltage, and power factor (RMS values).

I = \frac{P}{V \cdot PF}\ \text{(single-phase)}
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I = \frac{P}{\sqrt{3}\,V \cdot PF}\ \text{(three-phase, }V=V_{LL}\text{)}
  • Where I is the AC current (amps, RMS)
  • P is the real power (watts), and PF is the power factor (unitless)
  • V is the voltage (volts, RMS). For three-phase, use line-to-line (L-L) voltage.

To calculate AC current, divide real power by voltage and power factor (and by √3 for three-phase systems when using line-to-line voltage). Note: if you have a purely resistive load and know the power dissipated in the resistance, you can also use P = I2R (so I = √(P/R)) with RMS current.

How to Calculate AC Current?

The following two example problems outline how to calculate AC current.

Example Problem #1 (Single-Phase):

  1. First, determine the real power (watts). In this example, the real power is 1800 W.
  2. Next, determine the RMS voltage and the power factor. For this problem, V = 120 V and PF = 1.00.
  3. Finally, calculate the AC current using the formula above.

I = P / (V × PF)

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

I = 1800 / (120 × 1.00) = 15.0 (amps)

Example Problem #2 (Three-Phase): 

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

real power (watts) = 10,000

voltage (volts, line-to-line RMS) = 480

power factor = 0.90

Entering these values into the formula above gives : 

I = 10,000 / (√3 × 480 × 0.90) = 13.37 (amps)