The difference between kVA and kW comes down to power factor: kW is the real power a generator delivers to do work, kVA is its total apparent power, and kW = kVA × power factor. Because power factor is never above 1, a generator’s kVA figure is always equal to or higher than its kW figure.
What Is kW on a Generator?
A kilowatt (kW) is 1,000 watts of real power, also called active or true power. It is the portion of electricity that actually does work: running a motor shaft, producing light, heating an element or charging a battery.
The kW figure is the one that matches the power draw printed on most appliances (in watts), and it is also what the generator’s engine has to supply. Every kilowatt of real power requires mechanical power from the engine plus fuel, so kW is the number that ties directly to fuel consumption and engine size.
When you add up the running watts of the tools and appliances you want to power, you are adding up kW.
What Is kVA on a Generator?
A kilovolt-ampere (kVA) is 1,000 volt-amperes of apparent power: the product of the voltage and the current the generator’s alternator supplies. It describes the total electrical load the alternator can carry, whether or not that load turns it into useful work.
Some loads, mainly motors, compressors, transformers and fluorescent lighting, draw extra current that builds magnetic fields instead of producing work. This is called reactive power. It still flows through the windings and cables and still heats them, so the alternator has to be sized for it. kVA captures real power and reactive power together.
An easy way to picture it is a glass of beer: the liquid is the real power (kW), the foam is the reactive power, and the full glass is the apparent power (kVA).
kVA vs kW: Key Differences
| kW (kilowatt) | kVA (kilovolt-ampere) | |
|---|---|---|
| Type of power | Real (active) power | Apparent power |
| What it represents | Power converted into useful work | Real power plus reactive power |
| Calculated as | kVA × power factor | Volts × amps ÷ 1,000 (single-phase) |
| Limited by | The engine (fuel and mechanical output) | The alternator (windings and current capacity) |
| Matches | Appliance wattage labels | Alternator and transformer ratings |
| Relationship | Always ≤ kVA | Always ≥ kW |
The two values are equal only when the power factor is 1, which is the case for purely resistive loads such as heaters and incandescent lamps, and is typical of the single-phase ratings of many small portable generators.
Power Factor and How to Convert kVA to kW
Power factor (PF, or cos φ) is the ratio of real power to apparent power. It is a number between 0 and 1 that tells you how much of the current is doing useful work. Generator makers commonly rate larger three-phase sets at a power factor of 0.8, meaning the engine is sized to deliver 80% of the kVA as kW.
- kW = kVA × PF
- kVA = kW ÷ PF
Worked examples:
- kVA to kW: a 10 kVA generator at PF 0.8 delivers 10 × 0.8 = 8 kW.
- kW to kVA: a load of 10 kW at PF 0.8 needs 10 ÷ 0.8 = 12.5 kVA of alternator capacity.
- Unity power factor: a 5 kVA generator rated at PF 1.0 delivers 5 × 1.0 = 5 kW.
| kVA rating | kW at PF 0.8 | kW at PF 0.9 | kW at PF 1.0 |
|---|---|---|---|
| 5 kVA | 4.0 kW | 4.5 kW | 5.0 kW |
| 7.5 kVA | 6.0 kW | 6.75 kW | 7.5 kW |
| 10 kVA | 8.0 kW | 9.0 kW | 10.0 kW |
| 15 kVA | 12.0 kW | 13.5 kW | 15.0 kW |
| 20 kVA | 16.0 kW | 18.0 kW | 20.0 kW |
The current a generator can supply also follows from kVA. For a single-phase unit, amps = kVA × 1,000 ÷ volts. For a three-phase unit, amps = kVA × 1,000 ÷ (volts × 1.732).
Why Generators Are Rated in Both kVA and kW
A generator is two machines in one, and each has its own limit:
- The engine limits kW. It can only turn so much fuel into shaft power. Pushing real power past the engine rating causes overload, stalling or damage.
- The alternator limits kVA. Its windings can only carry so much current before they overheat, regardless of how much of that current does useful work.
A generator therefore has two ceilings, and your load must stay under both. A load with a low power factor (a large induction motor, for example) can reach the kVA ceiling while the engine is still lightly loaded. A purely resistive load can reach the kW ceiling first.
Ratings can also change with operating conditions. Altitude, high ambient temperature and fuel type can reduce the kW a generator can deliver, so it is worth checking whether a published rating applies to your conditions and fuel.
How kVA and kW Appear on Real Generator Specifications
Two hybrid (LPG / natural gas / petrol) models from GRETECH show the two common labelling styles.
Three-phase: both kW and kVA are listed. The JLY-10000I three-phase hybrid generator publishes its output at 400 V in both units. The ratio of kW to kVA is about 0.8 in every row, which is the conventional three-phase power factor.
| Fuel | Rated power at 400 V | Max power at 400 V | Implied PF |
|---|---|---|---|
| LPG / petrol | 8.5 kW / 10.6 kVA | 9.0 kW / 11.2 kVA | about 0.80 |
| Natural gas | 7.5 kW / 9.4 kVA | 8.5 kW / 10.6 kVA | about 0.80 |
Two points stand out. First, the kVA figure is about 25% higher than the kW figure, so a buyer comparing only kVA numbers across brands could overestimate usable power. Second, the rating changes with fuel: this model gives roughly 1 kW less rated output on natural gas than on LPG or petrol, which is normal for engines converted to run on gaseous fuels.
Single-phase: output listed in watts. The JLY-6500 single-phase hybrid generator lists its output in kW directly (5.0 kW rated and 5.5 kW maximum on LPG or petrol, 4.5 kW rated and 4.8 kW maximum on natural gas) at 230 V with a power factor of 1. With cos φ = 1, the kVA and kW values are numerically the same, so no conversion is needed.
When specs are written differently across brands, the simplest check is to convert everything to rated kW at the same fuel and voltage before comparing.
How to Size a Generator Using kW and kVA
Size the generator on the real power you need, then confirm the kVA is adequate for your power factor.
- List every load you want to run at the same time, with its running power in watts (from the nameplate) and, if known, its power factor.
- Add up the running kW. Convert each load to kVA (kW ÷ PF) and add those up as well.
- Allow for starting surge. Motors, pumps and compressors briefly draw several times their running current. Add the largest starting demand on top of the other running loads, using the figure on the equipment label or from the manufacturer.
- Add a safety margin of roughly 20–25% so the generator does not run at its limit continuously.
- Compare with the rated values, not the peak values, at your fuel type, voltage and phase. Check both the kW (engine) and the kVA (alternator) ratings.
Illustrative example (typical figures, not measured):
| Load | Running kW | Power factor | kVA |
|---|---|---|---|
| Lighting and electronics | 0.8 | 1.00 | 0.80 |
| Refrigerator | 0.3 | 0.80 | 0.38 |
| Water pump | 1.1 | 0.80 | 1.38 |
| Air conditioner | 2.0 | 0.85 | 2.35 |
| Total | 4.2 | 0.86 combined | 4.90 |
Adding a 25% margin gives about 5.25 kW and 6.1 kVA of required rated capacity, before the starting surge of the pump and air conditioner is considered. A generator rated at 5.0 kW would therefore be too small for this load, even though its kVA rating might look sufficient on paper.
If you want a unit that can run on LPG or natural gas as well as petrol, compare candidates on the hybrid generators page using the rated kW for your preferred fuel.
Common Mistakes When Comparing kVA and kW
- Treating kVA as kW. A 10 kVA generator at PF 0.8 supplies 8 kW, not 10 kW. Always convert before comparing models.
- Comparing peak with rated figures. Max (peak) output can be sustained only briefly. Use the rated, continuous value for sizing.
- Ignoring the fuel. On multi-fuel generators, output on natural gas or LPG can differ from output on petrol.
- Forgetting starting surge. The running load may fit while the start-up of a single motor trips the breaker or stalls the engine.
- Mixing phases and voltages. A three-phase kVA rating cannot simply be applied to a single-phase circuit. Check the voltage and phase of each output.
- Oversizing by a wide margin. A generator running far below its rating wastes fuel and can run less efficiently, so aim for a sensible margin, not the biggest unit available.
kVA vs kW Generator FAQ
Is kVA bigger than kW? Yes, or equal. Power factor cannot exceed 1, so kVA is always at least as large as kW.
How many kW is a 10 kVA generator? At the common three-phase power factor of 0.8 it is 8 kW. At a power factor of 1.0 it is 10 kW. The nameplate power factor decides.
Is 5 kVA the same as 5 kW? Only when the power factor is 1. For a generator rated at PF 0.8, 5 kVA is 4 kW.
Which matters more when buying a generator, kW or kVA? Both are limits, but kW is the better starting point because it reflects the engine and the real power your appliances use. Then confirm the kVA covers motor and other inductive loads.
Why do manufacturers advertise kVA first? kVA is the alternator rating and the number is larger. It is accurate, but it must be converted to kW to compare power output properly.
Can I run a generator on a load larger than its kVA rating? No. Exceeding the kVA or the current rating overheats the alternator windings, and the breaker will trip or the unit may be damaged.
Do kW and kVA change with the fuel used? The alternator’s kVA capacity does not depend on fuel, but the engine’s kW output can. Multi-fuel generators publish separate ratings for each fuel.
Conclusion
kW tells you how much useful power a generator’s engine can deliver; kVA tells you how much total current the alternator can handle; and the power factor connects them. To choose correctly, convert every rating to rated kW at your fuel, voltage and phase, add up your running load with a margin for starting surge, and confirm the kVA is sufficient for any motor loads.
If you are comparing LPG, natural gas or petrol models and want help matching a generator to your load, you can send your requirements through the contact form on any GRETECH hybrid generator page.