kVA to kW / Power Factor Calculator
Enter any two values — kVA, kW or power factor — to calculate the third. Also find kVAR reactive power for AC power system analysis.
Reviewed by the ToolNestr Editorial Team — July 2026
How kVA to kW conversion works
In AC power systems, apparent power (kVA) and real power (kW) are related by the power factor: kW = kVA × PF. Apparent power is the total power supplied by the source, while real power is the portion that does useful work. The difference is reactive power (kVAR), which sustains magnetic fields in inductive loads but does no work.
The relationship follows the power triangle: kVA² = kW² + kVAR², and PF = kW / kVA = cos(θ), where θ is the phase angle between voltage and current. Improving power factor from a low value toward unity reduces current for the same real power, lowering I²R losses and avoiding utility penalties.
Worked example
What different power factor correction levels mean
Power factor correction improves system efficiency. Here is how different PF levels affect your electrical system.
Facility Manager
Monitor and track power factor across your facility to avoid utility penalties and optimize energy costs.
Generator Operator
Size generators correctly by converting load kW to kVA at the expected power factor to ensure adequate capacity.
Utility Engineer
Analyze customer load profiles and determine power factor penalty structures for industrial and commercial accounts.
Solar Installer
Verify that inverter power factor settings match grid requirements and that solar generation does not cause PF issues.
| Motor rating (HP) | kW approx | Typical PF | Required kVAR correction | Capacitor size (μF @ 480V) |
|---|---|---|---|---|
| 5 HP | 3.7 kW | 0.80 | 2.8 kVAR | 38 μF |
| 10 HP | 7.5 kW | 0.82 | 5.2 kVAR | 72 μF |
| 25 HP | 18.7 kW | 0.84 | 12.1 kVAR | 167 μF |
| 50 HP | 37.3 kW | 0.86 | 22.1 kVAR | 306 μF |
| 100 HP | 74.6 kW | 0.88 | 40.3 kVAR | 557 μF |
| 200 HP | 149 kW | 0.90 | 72.2 kVAR | 998 μF |
How to use the kVA to kW Calculator
Enter any two values
Type in any two of the four values: kVA, kW, power factor, or kVAR. The remaining fields compute automatically.
Verify the power triangle
Check that the displayed kVA, kW and kVAR satisfy the power triangle relationship. The phase angle shows the lead/lag condition.
Plan correction if needed
If power factor is below your utility\u2019s threshold, use the kVAR result to size correction capacitors and improve efficiency.
Tips for power factor management
Know your utility\u2019s PF threshold
Most utilities set a power factor penalty threshold between 0.85 and 0.90. Check your utility tariff to know the exact value and avoid unexpected charges on your bill.
Automatic correction banks are worth it
For facilities with variable loads, automatic PF correction banks with multiple capacitor stages adjust to maintain target PF. The investment often pays back in 1\u20133 years through penalty avoidance.
Avoid over-correction
Adding too many capacitors can make the PF leading, which can cause over-voltage conditions, harmonic resonance, and damage to equipment. Target a PF of 0.95\u20130.98 lagging for best results.
VFDs improve PF naturally
Variable frequency drives include built-in DC bus capacitors that provide power factor correction. A VFD-driven motor often has PF of 0.95+ without external capacitors, reducing the need for dedicated correction equipment.
Apparent vs real vs reactive power
In AC power systems, the total power supplied by the source is called apparent power (S), measured in kVA. Only part of this power does useful work \u2014 this is real power (P), measured in kW. The remainder, reactive power (Q), measured in kVAR, flows back and forth between the source and magnetic fields in inductive loads. The vector sum of real and reactive power gives apparent power: S\u00b2 = P\u00b2 + Q\u00b2.
Power factor formula
Power factor is defined as PF = P / S = kW / kVA. It is also the cosine of the phase angle between voltage and current: PF = cos(\u03b8). For sinusoidal AC systems, \u03b8 = arccos(PF). The reactive power can be calculated as Q = S \u00d7 sin(\u03b8) or Q = \u221a(S\u00b2 - P\u00b2).
Why power factor matters
Low power factor has several negative consequences: increased current for the same real power, causing higher I\u00b2R losses in conductors; larger voltage drops in distribution systems; reduced capacity of transformers and generators; and utility penalties that can add 10\u201330% to the electric bill. Improving PF from 0.70 to 0.95 reduces current by about 26% and eliminates most penalties.
How to correct power factor
Power factor correction involves adding capacitors in parallel with inductive loads. The required capacitance in kVAR is Q_correct = P \u00d7 (tan(\u03b8_initial) - tan(\u03b8_target)). For a 500 kW load improving from 0.80 to 0.95 PF, about 187 kVAR of capacitance is needed. Automatic capacitor banks with power factor controllers switch stages in and out to maintain the target PF as load varies.
Frequently asked questions
What is the difference between kVA and kW?
kVA (kilovolt-amps) is apparent power, which is the total power supplied by the source. kW (kilowatts) is real power, which is the actual power consumed by the load doing useful work. The difference is reactive power (kVAR), which sustains magnetic fields but does no work.
How do I convert kVA to kW?
Multiply kVA by the power factor: kW = kVA × PF. For example, 100 kVA at 0.8 PF = 80 kW. Without knowing the power factor, you cannot accurately convert kVA to kW.
What is power factor?
Power factor is the ratio of real power (kW) to apparent power (kVA): PF = kW / kVA. It ranges from 0 to 1 and indicates how efficiently the electrical power is being used. A PF of 1.0 means all power is doing useful work.
What causes reactive power (kVAR)?
Reactive power is caused by inductive loads such as motors, transformers, and fluorescent lighting ballasts, which require magnetic fields to operate. These fields store and release energy each AC cycle, creating a phase shift between voltage and current.
How are kVA, kW and kVAR related?
They form a right-triangle relationship: kVA² = kW² + kVAR². kVA is the hypotenuse, kW is the adjacent side (real power), and kVAR is the opposite side (reactive power). Power factor is cos(θ) = kW / kVA.
Why do utilities charge for power factor?
Low power factor means higher current for the same real power, which requires larger transformers, switchgear, and wiring. Utilities add PF penalties to recover these infrastructure costs. Typical PF thresholds are 0.85 to 0.90.
What is a typical power factor for a generator?
Generators are typically rated at 0.8 PF. This means a 500 kVA generator can supply 400 kW continuously. Operating above the rated PF may overheat the generator, while operating below it under-utilizes the machine.
How do I improve power factor?
Add power factor correction capacitors in parallel with inductive loads. Capacitors supply leading reactive power that cancels the lagging reactive power of motors and transformers. Automatic PF correction banks switch capacitor stages as needed.
What is the power triangle?
The power triangle graphically shows the relationship between kW (horizontal), kVAR (vertical), and kVA (hypotenuse). The angle between kW and kVA is the phase angle θ, and cos(θ) = PF. Vector addition of kW and kVAR gives kVA.
Can power factor be leading?
Yes, when capacitive loads exceed inductive loads, power factor becomes leading. While utilities prefer near-unity PF, slightly leading PF is generally acceptable. Large installations with extensive capacitor banks can become leading during light load periods.
Sources & references
This tool uses standard formulas and reference values from:
- • NFPA 70 — National Electrical Code (NEC), conduit fill, box fill and conductor ampacity. nfpa.org
- • IPC-2221, Generic Standard on Printed Board Design (trace width / current). ipc.org
- • NIST reference constants and unit definitions; IEEE standards where applicable. nist.gov
For educational and preliminary use. Verify against full engineering calculations and the governing standard before any real design.