kVA versus kW
Definition. kW measures the real power that does useful work, kVA measures the apparent power the network must actually supply, and the ratio between them is the power factor — which is why a 10 kVA supply cannot always deliver 10 kW.
Also called: Apparent power · Real power · Reactive power · kVAR
Where you see it: On sanctioned load records, generator and UPS nameplates, and demand charges on industrial bills.
The relationship
kW = kVA × power factor. At a power factor of 0.8, a 10 kVA generator delivers 8 kW of real power, which is why the generator that comfortably ran a resistive load struggles with a motor load of the same nominal size.
Purely resistive loads — heaters, filament lamps, irons — sit at a power factor of about 1, so their kW and kVA figures are effectively the same.
Why sizing goes wrong
People add up the watt ratings of everything they want to run and buy a generator of that many kVA. That understates the requirement whenever motors are involved, and it ignores motor starting current, which can briefly reach several times running current.
Size on the kVA figure with the site's real power factor applied, and allow headroom for the largest motor's start.
On the bill
Where a tariff levies demand charges in kVA, poor power factor directly increases the billed demand for the same useful output. Correcting it lowers kVA without changing kW.
Where demand is charged in kW, power factor affects the separate penalty line instead.
Frequently asked questions
Which figure should I use to size a UPS or inverter for my home?
Total the watt ratings of what must run, then divide by the unit's power factor — commonly 0.8 on a domestic inverter — to get the kVA rating required, and add headroom for surge on any motor loads such as a water pump or a refrigerator compressor.
Is my sanctioned load in kW or kVA?
Domestic sanctioned load is normally recorded in kW. Industrial connections are frequently recorded and billed in kVA, which is stated on the connection agreement.
Related terms
- Power factor — What causes poor power factor in a Pakistani industrial connection, how the penalty is calculated, and whether a capacitor bank pays for itself.
- Kilowatt-hour — The difference between a kilowatt and a kilowatt-hour, why appliance labels quote watts but bills quote units, and how to convert between them.
- Sanctioned load — The difference between connected and sanctioned load, what happens when you exceed the sanctioned figure, and how to apply to change it in either direction.
- Maximum demand indicator — Why commercial and industrial bills charge for a single half hour of the month, how MDI is measured, and the practical ways to bring the recorded peak down.
Go further
Back to the full 44-term glossary, or open your own bill with the reference number lookup.