What is kVa?

If you’re like most people, you’re familiar with watts and kilowatts from purchasing home appliances and kilowatt-hours (kWh) from your electricity bills.

But what about volt-amperes (Va) and kilovolt-amperes (kVA)?

No?

You’re not alone.

Unless you’ve been shopping for a generator or uninterruptible power supply (UPS), you’ve probably never come across kVa as a specification before.

So, what is KVA?

kVA measures apparent power.

Still in the dark?

Not for long!

Learn more about kilovolt-amperes, how to convert KVA to kilowatts, and why kVa matters when purchasing a UPS, battery backup, or a generator.

What’s the Difference Between kW and kVa?

Kilowatts and kilovolt-amperes are both measurements of power.

Watts (W) and kilowatts (kW) measure the actual electricity output of a generator or other power source — frequently called working power.

Volt-amps and kilovolt-amps measure the apparent power a generator produces without accounting for the system’s inefficiency. 

Another way of thinking about the difference between apparent power and working or “real” power is as the difference between the energy (fuel) consumed relative to the electricity output.

No machine or electrical system is 100% efficient.

In fact, it’s an impossibility.

Or is it? (Yes).

People have been trying to build perpetual motion machines since the Middle Ages, but thanks to the Laws of Thermodynamics, they always fail.

Without going too far down the rabbit hole, many electrical systems approach 100% efficiency, but conventional fossil fuel generators that output AC electricity aren’t one of them.

Not even close.

That’s why kVA — apparent power — is frequently used as a specification for power sources that produce electricity.

The system generates significantly more power (kVa) than it outputs as working electricity (watts or kW). 

What Is Power Factor (PF)?

Power factor measures electrical efficiency on a scale of zero to one, with 1 indicating 100% efficiency and 0 equaling none.

Many electrical systems — such as DC-to-DC generators, RV Power Kits, and utility-grid scale transformers — approach 100% efficiency, but conventional fossil fuel generators that output alternating current (AC) electricity are not among them.

Most gas, propane, and diesel-powered generators have a power factor of 0.8 (80%).

The formula for electrical efficiency is:

Efficiency = Useful Power Output / Total Power Input

For example, a generator that outputs 2000W AC but burns the equivalent of 2400W of fuel is 80% efficient and has a power factor of 0.8.

The concept of electrical efficiency can be difficult to grasp.

For example, incandescent lightbulbs are only about 2% efficient at lighting up a room but close to 100% efficient at heating it. 🤯

Feel free to do a deep dive into electrical efficiency here.

When it comes to Power Factor (PF) being a useful spec, it allows you to calculate the kilowatts a generator or battery system will output in watts vs. how much power it consumes to produce it (volt-amps and kVa).

How Is kVA Calculated?

Calculating kilovolt-amps isn’t too much of a challenge if you’re studying physics… 

However, if you’re not, it’s unlikely that you’ll ever need to measure kVa yourself.

If you’re interested in how kVa and power factor impact the efficiency of a generator or battery system, the manufacturer will likely provide you with both specs.

In which case, you can use the kVa to kilowatt conversion methods and calculators below to understand how it will impact the system’s efficiency.

Here are the formulas for calculating kVa, just in case.

Single-Phase Power System

Calculating kilovolt amps requires two pieces of information about the system.

1. Load Line to Line Voltage (V)
2. Maximum Load Phase Current (I)

Once you have those specs, the formula is:

Voltage (V) × Current (I) = kVa

1000 

For example

3-Phase Power System 

The basic formula for calculating the kilovolt-amps of a 3-phase power system uses the same specs as for a single-phase system divided by the square root of three.

Voltage (V) × Current (I) x √3 = kVa

1000 

For example

Calculating the kVa of a 3-phase system with line-to-line or line-to-neutral voltage requires additional steps:

3-Phase Power System With Line-To-Line Voltage

Line-to-Line Voltage (V) ×  Current (I) × √3 = kVa

1000

3-Phase Power System With Line-To-Neutral Voltage

Line-to-Neutral Voltage (V) ×  Current (I) × 3 = kVa

1000 

kVA to kW Conversion

If you know the kilovolt-amps and power factor (PF)of a generator, UPS, or battery power source, converting kVa to kilowatts is easy.

Here’s the formula:

kVa × pf = kilowatts

For example, a 5kVa generator with a power factor of 0.8 will have an AC or DC output of 4000W (4kW).

5kVa × 0.8 = 4000W (4kW)

kW to kVA Conversion

If you’d like to convert kilowatt hours to kilovolt-amps and you know real electrical output in watts and the power factor of the source, the formula is:

kilowatts / power factor = kilovolt-amps

For example, a 4000W (4kW) gas generator with a power factor of 0.8 will consume the equivalent of 5000W (5kW) of fuel.

In other words, 20% of the gas consumed is lost to system inefficiency.

Frequently Asked Questions

Final Thoughts

Although not nearly as widely used as watts, volts, and amps, kilovolt-amps are essential for evaluating the suitability and performance of electrical systems, particularly ones with inverters that convert power from AC to DC or vice versa.

If you’re shopping for a generator, it pays to check out more energy-efficient alternatives to conventional models.

Inverters and solar generators offer much better efficiency and performance than traditional generators.

Check out EcoFlow’s selection today.