Calculation sequence
Step-by-step method
- Multiply RMS voltage by RMS current for apparent power.
- Apply true power factor for real power.
- Calculate reactive-power magnitude from the power triangle.
ElectricalBeginnerElectrical Fundamentals
Single-Phase AC Power Calculator
Calculate apparent, real, and reactive-power magnitude for a measured single-phase AC load.
Why it matters: Voltage, current, real power, and apparent power are not interchangeable when power factor is below unity.
Calculated result
Engineering evaluation
Real power (P)3.84 kW
- Apparent power (S)
- 4.8 kVA
- Reactive-power magnitude (Q)
- 2.88 kvar
Engineering interpretation
The entered single-phase condition represents 3.84 kW, 4.8 kVA, and 2.88 kvar magnitude.
Important limitations
- Reactive-power direction is not inferred. Confirm leading or lagging operation and use true-power instrumentation for distorted waveforms.
Engineering knowledge center
Understand the calculation—not just the answer
Governing relationships
S = V·I/1000
P = S·PF
Q = S√(1−PF²)
Current substitution
S = 240×20/1000 = 4.8 kVA; P = 4.8×0.8 = 3.84 kW; Q = 2.88 kvar.
Equation legend
Inputs and calculated quantities
- V
- RMS voltage — V
- I
- RMS current — A
- PF
- True power factor — 0–1
- P
- Real power — kW
- S
- Apparent power — kVA
- Q
- Reactive-power magnitude — kvar
Applications
How this calculation is used
Building design
Screen single-phase load relationships.
Construction
Reconcile startup voltage, current, and power readings.
Commissioning
Check a measured single-phase operating point using true RMS values and true power factor.
Quality controls
Assumptions and limitations
Assumptions
- Entered values describe one stable operating condition and use a consistent electrical or metering boundary.
- Measured quantities are simultaneous, representative, and obtained with appropriately rated instruments.
Limitations
- Reactive power is reported as a magnitude unless the leading or lagging direction is separately known.
- Distorted waveforms require a true-power analyzer and appropriate power-quantity definitions.
Field use
Verification procedure
- Follow the approved electrical-safety program and use correctly rated instruments.
- Confirm wiring, ratios, units, operating mode, and measurement boundaries.
- Document simultaneous readings and compare with approved project and manufacturer data.
Common engineering mistakes
- Combining values from different time intervals, phases, or measurement boundaries.
- Treating a screening result as equipment selection, protective-device coordination, or code compliance.
Technical basis
References and source standards
- NIST Guide for the Use of the International System of UnitsElectrical quantity, unit, symbol, and conversion context.
- IEEE Standards AssociationPower quantity, harmonic, transformer, motor, battery, and metering standards; verify the current applicable edition during professional review.
Engineering calculation disclaimer
These engineering tools are provided for educational, preliminary evaluation, field verification, and commissioning support. Results depend on the accuracy of user-entered information and the assumptions stated for each calculation. Every colored status and comparison is a screening indicator only; project criteria, contract requirements, applicable codes, manufacturer instructions, measurement uncertainty, and authorized engineering judgment govern. The tools do not replace project-specific engineering analysis or the judgment of a licensed professional engineer.
Read the full use and limitation statement