Quick answer
Enter the exact apparent-power rating, line voltage, phase system, and power factor. For single phase, line current is kVA times 1,000 divided by volts. For balanced three phase, divide by the square root of three times line-to-line volts. Real kW is kVA times power factor. Use the result as nameplate arithmetic, not as a generator selection. Motor starts, nonlinear loads, phase imbalance, duty rating, fuel derating, and transient response require separate checks.
Keep kW, kVA, kVAR and power factor distinct
Real power in kW represents the portion doing useful work or heat. Apparent power in kVA combines voltage and current without reducing the result by power factor. Reactive power in kVAR represents the quadrature component in an idealized AC power triangle. Power factor relates real power to apparent power.
A generator alternator and engine can face different limits. The engine supplies real power, while alternator current and heating relate strongly to kVA. Compare both ratings and the manufacturer application data.
Select the formula from the actual electrical system
Use the single-phase formula for a single-phase load at its stated voltage. A North American 120/240-volt split-phase generator is still a single-phase source, and a 240-volt load uses single-phase math. The 120-volt legs also need a separate balance check.
Use the three-phase formula only for a balanced three-phase load with line-to-line voltage. Unbalanced phase currents must be evaluated by phase. Do not divide a single-phase load by the square root of three.
Use a power factor from the exact load condition
Power factor can change with motor loading, electronic drives, rectifiers, filters, and operating mode. A default value is an assumption, not a nameplate fact. When only kW is known, kVA equals kW divided by power factor, but uncertainty in power factor carries directly into the result.
Displacement power factor does not describe every harmonic effect. Nonlinear loads can draw distorted current that affects alternator heating, neutral current, voltage waveform, UPS behavior, and generator sizing beyond a simple scalar conversion.
Calculate starting and step loads separately
Motor starting may be stated as locked-rotor current, starting kVA, or a manufacturer generator-sizing requirement. Add the start event to other loads already operating and check voltage and frequency recovery. Continuous kVA conversion does not predict how long or how deeply the source voltage will dip.
Variable-frequency drives, UPS systems, battery chargers, and other constant-power or electronic loads can have input behavior that differs from a resistive bank. Use manufacturer data and approved sizing methods for those loads.
Finish the calculation with the physical power path
Verify generator duty rating, selected-fuel output, voltage, phase, frequency, outlet or terminal current, breaker, conductors, distribution, transfer equipment, grounding and bonding, ambient and altitude derating, and load balance. The smallest limit in the path controls.
Commission the system with representative steps and measure voltage, current by phase, frequency, kW, kVA and power factor where instrumentation supports them. Preserve the inputs and assumptions so the result can be reviewed after equipment or load changes.
Frequently asked questions
Common questions
How many amps is a 12 kVA generator at 240 volts?
For single phase, the arithmetic is 12,000 divided by 240, or 50 amperes. The actual usable current remains limited by the exact generator, outlet, breaker, duty, fuel, and conditions.
How do I convert kVA to kW?
Multiply kVA by the power factor at the same operating point. For example, 12 kVA at 0.8 power factor is 9.6 kW.
Is 120/240V split phase the same as three phase?
No. It is single phase with two 120-volt legs 180 electrical degrees apart. Use single-phase power math and check the 120-volt leg balance.
Can this calculator size a generator for a motor?
Not by itself. Motor starting kVA, duration, other running loads, voltage recovery, frequency response, duty, and manufacturer requirements must also be evaluated.
Primary references
CordFind summarizes connector specifications and public safety guidance. Always follow the instructions supplied with your equipment.