At a glance: kVA vs kW
- kVA and kW are both used to describe electrical power, but they measure different things.
- kVA means kilovolt-amperes and measures apparent power.
- kW means kilowatts and measures real power.
- Power factor links the two. The formula is kW = kVA × power factor.
- At a power factor of 1, kVA and kW are numerically equal. At a lower power factor, the kW figure will be lower than the kVA figure.
- Portable petrol and dual-fuel generators are often described in watts or kilowatts, while kVA is commonly used on larger generator specifications.
- Don’t compare kVA and kW figures at face value. Check the power factor and whether the figure refers to rated or maximum output.
- The right generator output depends on what you need to power, including any extra demand when equipment starts up.
If you're comparing generators, you'll probably see power output shown in kVA, kW or both. Knowing what those figures mean makes it much easier to compare models properly.
The key difference is simple: kVA measures apparent power, while kW measures real power. The two are linked by power factor, which is why a 10 kVA generator does not always provide 10 kW of real power.
For most buyers, you don't need to get too deep into the electrical theory. You need to know which figure you're looking at, how it relates to your equipment and whether the generator has enough output for the job.
kVA vs kW: what does each rating tell you?
The easiest way to understand the difference is to look at what each unit measures.
| Feature | kVA | kW |
|---|---|---|
| Stands for | Kilovolt-amperes | Kilowatts |
| Measures | Apparent power | Real power |
| Takes power factor into account? | No | Yes, when converting from kVA |
| Where you may see it | Generator and electrical system ratings, particularly larger equipment | Generator output, appliances, tools and other electrical equipment |
| Useful for | Understanding total apparent power capacity | Understanding real power available to do useful work |
That difference matters when you’re comparing generator specifications. Two figures can look similar without representing the same amount of real power.
How do you convert kVA to kW?
To convert between the two, you need to know the power factor.
The formula is:
kW = kVA × power factor
So, for a 10 kVA generator rated at a power factor of 0.8:
10 × 0.8 = 8 kW
To work in the opposite direction:
kVA = kW ÷ power factor
For example, an 8 kW requirement at a power factor of 0.8 would be:
8 ÷ 0.8 = 10 kVA
The calculation itself is straightforward. The important part is using the correct power factor rather than assuming one. Check the generator specifications and the requirements of the equipment you're planning to power.
Why does power factor matter?
Power factor describes the relationship between real power and apparent power. It's expressed as a number between 0 and 1.
At a power factor of 1, 1 kVA is equivalent to 1 kW. If the power factor is lower, the real power in kW will also be lower than the apparent power figure in kVA.
This becomes especially important when you’re dealing with equipment such as motors and transformers. It also explains why simply looking at the biggest number on a generator specification can be misleading.
If you’d like a more detailed explanation of kVA itself, we've covered the terminology separately.
Why are portable generators often rated in watts or kW?
When you’re looking at a petrol generator or dual-fuel generator, you’ll often see the output stated in watts or kilowatts.
That can make comparison easier because many appliances and tools also state their power requirements in watts.
For example, if you know the combined running wattage of the equipment you want to use, you can compare that figure with the generator’s rated output.
You’ll still need to allow for any extra starting demand, but using the same units makes it easier to see whether the generator has enough capacity.
If you’re considering a dual-fuel model, check the output figures for the fuel you plan to use rather than relying on the headline specification alone.
Where are you more likely to see kVA?
You'll commonly come across kVA when looking at larger generators and electrical systems, including diesel generators designed for heavier-duty applications.
That doesn't mean kVA is a measurement reserved for diesel. It's simply a way of expressing apparent power and becomes particularly useful where power factor needs to be taken into account.
For many portable and general-purpose generator buyers, watts and kW will be the figures you deal with most often. If you're looking at a specification in kVA, make sure you understand its corresponding kW output before deciding whether it meets your needs.
Rated output vs maximum output: another difference to check
kVA and kW aren’t the only figures you need to understand when comparing generators. It’s also important to check whether the specification refers to rated output or maximum output.
Rated or continuous output is the figure to use when assessing the power a generator is designed to provide during normal operation.
Maximum or peak output is higher, but it isn’t intended to represent the load the generator can continuously supply.
So, if one generator is advertised using its maximum output and another uses its rated output, comparing those figures won’t give you a like-for-like comparison.
Which rating should you use when choosing a generator?
Start with the equipment you need to power rather than the generator specification.
Work out what you'll run at the same time and add up the running wattage. Then check whether any tools or appliances have a higher starting wattage.
Motors, pumps and compressors, for example, can briefly need more power when they start.
From there, you can compare your requirements with the generator's rated output. If that output is stated in kVA rather than kW, use the specified power factor to make the comparison.
kVA vs kW: what should you remember?
You don't need to memorise every electrical term to compare generator output ratings. Keep these points in mind:
- kVA measures apparent power.
- kW measures real power.
- Power factor connects the two.
- Don't assume that 1 kVA always equals 1 kW
- Check whether a specification shows rated or maximum output
- Account for both running and starting power requirements
- Compare the generator's usable output with the equipment you actually need to run
Once you know what each figure represents, generator specifications become much easier to compare.
Need help comparing generator output?
If you’re comparing kVA and kW ratings and aren’t sure which generator has the output you need, use our chat system to help you understand the specifications, work through your power requirements and narrow down the right generator for your setup.
