Potência Aparente S
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
Formula
S = VI
About this calculator
The apparent power calculator S determines the total power supplied to an alternating current circuit, calculated as the product of the effective voltage (V) and effective current (I). Unlike real power (P), which considers the power factor, apparent power represents the total system capacity, including active and reactive components. It is expressed in volt-amperes (VA) and is essential for sizing transformers, generators, and cables.
The calculation follows the formula S = V × I, where V is voltage in volts and I is current in amperes. For balanced three-phase systems, total apparent power is S = √3 × Vline × Iline. The calculator accepts voltage and current values in units such as V, kV, A, kA and returns results in VA, kVA, or MVA, facilitating use across different scales.
This tool is useful for electrical engineers, technicians, and students who need to size equipment or analyze power systems. For example, when specifying a transformer, apparent power determines its rated capacity. It is also used in electrical installation projects to verify if cables and circuit breakers can handle the total load.
Important precautions: apparent power does not consider the power factor, so it should not be confused with active power. In circuits with reactive loads (motors, ballasts), apparent power will be greater than active power. Always ensure voltage and current values are RMS. For three-phase systems, make sure to use the correct line voltage.
Frequently asked questions
What is the difference between apparent power and active power?
Apparent power (S) is the product of voltage and current, measured in VA. Active power (P) is the actual power consumed, measured in watts, and depends on the power factor (P = S × cos φ).
How to convert kVA to kW?
Multiply the kVA value by the power factor (cos φ). For example, 10 kVA with a power factor of 0.8 equals 8 kW.
Why is apparent power important for generators?
Generators are rated in kVA because they must supply apparent power to loads with different power factors. A 100 kVA generator can provide up to 100 kVA regardless of the load's power factor.
Can I use this calculator for three-phase circuits?
Yes, as long as you enter the line voltage and line current. The calculator automatically applies the √3 factor for balanced three-phase systems.
What does RMS mean and why use it?
RMS (Root Mean Square) is the effective value of alternating voltage or current. Using RMS values ensures the apparent power calculation is correct, as they represent the DC equivalent that produces the same power.