kW to kVA Calculator
Enter real power in kilowatts and the power factor to get apparent power in kVA and reactive power in kVAR — the figures you need to size generators, transformers, and UPS systems.
Generator and transformer sizing
Generators and transformers are rated in kVA, not kW. Converting your kW load to kVA is the first step in selecting the right unit for your installation.
Power factor must be known
This calculator assumes a constant, known power factor. If you do not know the power factor of your load, check the equipment nameplate or data sheet before sizing protective equipment.
What is the kW to kVA conversion?
Real power, apparent power, and the power factor link
Kilowatts (kW) measure real power — the energy per second that does actual work, such as spinning a motor or heating a room. Kilovolt-amperes (kVA) measure apparent power — the total electrical demand placed on the supply, including both the working and non-working components. The ratio between the two is the power factor (PF), a number from 0 to 1: kVA = kW ÷ PF. A lower power factor means a larger gap between real and apparent power, which means bigger cables, a larger generator, and potentially a utility surcharge.
Enter the real power in kW and the power factor to get the apparent power in kVA and the reactive power in kVAR instantly.
Divide the real power by the power factor to get the apparent power. The reactive power — the non-working component stored and released by inductive or capacitive loads — follows from the power triangle.
kVA = kW ÷ PF kVAR = √(kVA² − kW²)At a power factor of 0.8 — a common value for motors and mixed commercial loads — an 8 kW load draws 8 ÷ 0.8 = 10 kVA. The reactive component is √(10² − 8²) = √36 = 6 kVAR. When the power factor is 1.0 (purely resistive load), kVA equals kW exactly and reactive power is zero: a 100 kW resistive heater draws exactly 100 kVA. Improving the power factor from 0.8 to 0.9 on that same 8 kW load reduces the required kVA from 10 to 8.89 — a saving that directly reduces generator or transformer size.
The apparent power figure in kVA is the number to use when selecting a generator, UPS, or transformer. Equipment manufacturers rate these devices in kVA because the full current drawn by the load — including the reactive component — flows through their windings and determines their thermal rating, regardless of how much of that current does useful work. A generator rated at 10 kVA can safely supply the 8 kW load in the example above, but a 9 kVA unit would be under-rated by 10 %. As a practical rule, add a 20–25 % safety margin on top of the calculated kVA when sizing a generator for continuous operation, to allow for startup surges and future load growth. The reactive power figure in kVAR indicates how much of the supply capacity is wasted on maintaining magnetic or electric fields rather than delivering real work; reducing it through power factor correction capacitors can lower energy costs and reduce the required kVA rating of supply equipment.
This calculator assumes a single-phase or balanced three-phase load with a constant, known power factor.
Power factor below 1 inflates the kVA demand
Industrial and commercial loads — motors, variable-speed drives, welding equipment, and switching power supplies — typically have power factors between 0.7 and 0.95. A lower power factor means more apparent power (kVA) must be supplied for the same real load (kW), which increases the required size and cost of generators and transformers. Utilities in many countries apply a power factor surcharge when the site average falls below a threshold such as 0.95. Power factor correction capacitors can bring the factor closer to 1.0 and reduce both the kVA demand and any associated tariff penalties.