Single-phase
S = V x I
P = S x PF
Q = √(S2 - P2)
Electrical calculator
AC Power Calculator
Calculate kW, kVA, kVAR, and phase angle for single-phase or balanced three-phase AC circuits.
Instant AC power solver
Enter circuit values
Results update automatically. For three-phase systems, use line-to-line voltage and line current.
Calculated result
Formulas
AC power formulas used
Three-phase
S = √3 x V x I
P = √3 x V x I x PF
Q = √(S2 - P2)
Use volts and amps as base inputs. The calculator converts mV, kV, mA, and kA before solving, then reports power in kW, kVA, and kVAR.
Worked example
Example: 480 V three-phase motor load
Suppose a balanced three-phase motor circuit uses 480 V line-to-line, draws 32 A, and has a 0.86 power factor.
Apparent power
S = sqrt(3) x 480 x 32
S = 26.60 kVA
Real power
P = 26.60 x 0.86
P = 22.88 kW
Reactive power
Q = sqrt(S2 - P2)
Q = 13.56 kVAR
This means the supply equipment must carry about 26.60 kVA, while the load converts about 22.88 kW into useful electrical input power. Mechanical shaft output would be lower after motor losses.
Guide
How to use this AC power calculator
- Select single-phase or three-phase. For three-phase, enter line-to-line voltage.
- Enter voltage, current, and power factor. Power factor must be between 0 and 1.
- Read real power, reactive power, apparent power, phase angle, and the entered load summary.
Reference
What the results mean
Real power (kW)
The usable power converted into work, heat, light, or mechanical output by the load.
Reactive power (kVAR)
The oscillating power associated with magnetic and electric fields in inductive or capacitive loads.
Apparent power (kVA)
The total AC power capacity required from the source, transformer, generator, or distribution equipment.
Power factor
The ratio of real power to apparent power. A higher value means the system uses supplied power more effectively.
Assumptions and limits
Before using the result for design
- Three-phase calculations assume a balanced load using line-to-line voltage and line current.
- The calculator reports electrical input power. It does not include motor efficiency, drive losses, harmonic distortion, demand factors, or service factor.
- Power factor is treated as a positive magnitude from 0 to 1. It does not distinguish leading and lagging loads.
- Use applicable electrical codes, equipment nameplates, manufacturer data, and qualified engineering judgement for conductor, breaker, generator, transformer, and motor sizing.
Useful next checks
Related engineering tasks
Check voltage drop
After estimating current and power, verify conductor voltage drop for the circuit length and wire size.
Open voltage drop calculatorReview power factor
Low power factor can increase apparent power demand and current for the same useful kW load.
Open power factor calculatorEstimate wire size
Use current, voltage, phase arrangement, and allowable voltage drop when selecting conductors.
Open wire size calculatorCalculate basic circuit values
For resistive or DC-equivalent checks, calculate voltage, current, resistance, and power with Ohm's law.
Open Ohm's law calculatorFAQ
AC power calculator questions
What is the difference between kW, kVA, and kVAR?
kW is real power, kVA is apparent power, and kVAR is reactive power. Together they describe the AC power triangle.
Can I use this calculator for motors?
Yes, it is useful for estimating motor electrical input power when you know voltage, current, phase type, and power factor. It does not replace nameplate data, efficiency data, service factor, or code-based sizing.
Why does three-phase power use square root of 3?
The square-root-of-3 factor comes from the 120-degree phase separation in a balanced three-phase system when using line voltage and line current.
Does this calculator include motor efficiency?
No. The result is electrical input power. Mechanical shaft output requires motor efficiency or measured output data.
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