When to Use This Calculator
Use this calculator for a steady-state single-phase AC load when RMS voltage, RMS current, and power factor are known. It is useful for panel checks, small equipment loads, transformer loading, and comparing kW with kVA.
Enter Values
Formula Summary
kW = V × A × PF ÷ 1000
kVA = V × A ÷ 1000
PF is the power factor from greater than 0 through 1.
Practical Examples
240 V equipment load
At 240 V, 20 A, and 0.90 PF, real power is 4.32 kW and apparent power is 4.80 kVA.
120 V branch load
At 120 V, 12 A, and 0.95 PF, real power is 1.37 kW and apparent power is 1.44 kVA.
Understanding the Inputs
- Voltage: RMS voltage across the single-phase load.
- Current: RMS current drawn by the load.
- Power factor: real power divided by apparent power, from greater than 0 through 1.
For a nearly resistive load, power factor may be close to 1. Motors, transformers, and electronic equipment can have lower power factor.
What the Results Mean
Kilowatts measure real power converted into useful work or heat. Kilovolt-amperes measure apparent power carried by the source and conductors. A low power factor increases current and kVA for the same real power.
This calculator does not include efficiency. If you start with mechanical output power, include equipment efficiency before comparing it with electrical input power.
Common Mistakes
- Using DC watts formulas without including AC power factor.
- Entering peak voltage or current instead of RMS values.
- Comparing kW to equipment kVA ratings without accounting for power factor.
- Using calculated running load as the only basis for conductor or breaker sizing.
Reference Notes
The formulas are standard single-phase AC apparent-power and real-power relationships. Equipment and installation sizing should be checked against nameplates, manufacturer instructions, and the applicable electrical code.