kVA, kW, Amps & Watts Explained

The right size always depends on:

• total running load
• startup load requirements
• single phase or 3 phase equipment
• runtime expectations
• future expansion requirements

For larger commercial setups, it is often best to speak with a generator specialist to ensure the generator is correctly sized for the application.

What Is kW?

kW stands for kilowatts and measures the real usable power available from a generator or electrical system.

While kVA measures apparent power, kW measures the actual working power used to run equipment, appliances, tools, and machinery.

This is the power that performs real work.

For example:

• powering a refrigerator
• running a welder
• operating air conditioning
• supplying lighting
• running compressors or pumps

In generator systems, kW is closely linked to the generator’s power factor.

Generators are often rated in both:

• kVA
• kW

Because the usable power output is usually lower than the total apparent power capacity.

kVA vs kW Explained

The difference between kVA and kW comes down to how electrical power is used within a system.

• kVA = apparent power
• kW = usable working power

The relationship between the two is based on power factor.

For most commercial diesel generators, a power factor of 0.8 is commonly used.

This means:

kW = kVA \times 0.8

Example Generator Power Conversion

For example, a 20kVA generator with a 0.8 power factor produces approximately 16kW of usable working power.

This is important when sizing generators for:

• construction sites
• temporary commercial power
• events
• backup power systems
• industrial equipment

Because some equipment creates reactive electrical loads, generators must account for both apparent power and usable power capacity.

Why Generators Use kVA Ratings

Generators are commonly rated in kVA because electrical systems rarely operate at a perfect power factor.

Equipment such as:

• compressors
• welders
• motors
• pumps
• air conditioning systems

…can create reactive power loads that affect total generator demand.

Using kVA ratings allows generator sizing to account for these varying load conditions more accurately.

This is especially important in commercial and industrial environments where multiple pieces of equipment may start and run at different times.

For smaller residential applications, the difference between kVA and kW may feel less noticeable. However, for construction sites, standby systems, temporary power setups, and commercial operations, understanding the difference becomes much more important.

kVA To Amps Explained

Amps measure electrical current flowing through a system. When sizing a generator, understanding amperage is important because many tools, appliances, and commercial systems are rated in amps rather than kVA or kW.

This is especially common with:

• air conditioning systems
• welders
• compressors
• pumps
• site equipment
• commercial machinery

Knowing how many amps a generator can supply helps determine whether it can safely power your equipment without overload issues.

How To Convert kVA To Amps

The number of amps a generator produces depends on:

• generator size
• voltage
• whether the system is single phase or 3 phase

Single phase and 3 phase systems calculate amps differently, which is why commercial and industrial generator sizing can become more complex.

For simplified generator sizing, the following examples provide approximate amp outputs commonly used across Australian generator applications.

Approximate kVA To Amps Conversion Table

These figures are approximate and can vary depending on:

• voltage
• generator configuration
• power factor
• load type
• equipment startup demand

For larger commercial or industrial setups, it is always recommended to confirm electrical load requirements with a qualified generator specialist or electrician.

Why Amps Matter In Generator Sizing

Many commercial and industrial electrical systems are designed around amperage limits.

For example:

• site distribution boards
• circuit breakers
• extension leads
• switchboards
• cable sizing
• temporary site power systems

…are often rated by amps rather than kVA.

If the generator cannot safely provide enough amperage during startup or peak demand, problems can occur including:

• breaker trips
• overheating
• voltage drops
• unstable power supply
• startup failures

This is especially important when running:

• welders
• compressors
• large motors
• HVAC systems
• pumps
• refrigeration systems

These types of equipment often have high startup currents that exceed their normal running load.

Single Phase vs 3 Phase Amp Draw

Single phase generators are commonly used for:

• homes
• small businesses
• food trucks
• portable equipment

3 phase generators are more commonly used for:

• construction sites
• industrial machinery
• commercial facilities
• large HVAC systems
• heavy-duty equipment

Because 3 phase power spreads electrical load across multiple phases, the amperage per phase is lower compared to single phase systems of the same generator size.

This allows larger commercial equipment to operate more efficiently and with improved load balancing.

What Are Watts?

Watts are the basic unit of electrical power. They measure how much energy a device consumes or produces at any given moment.

Most appliances and equipment are rated in watts, which is why understanding wattage is important when sizing a generator.

For example:

• LED light = 10–20 watts
• Refrigerator = 150–800 watts
• Microwave = 1,000–1,500 watts
• Circular saw = 1,200–1,800 watts
• Air conditioner = 2,000+ watts

When generator loads become larger, watts are usually expressed as kilowatts (kW).

1kW = 1,000 watts

This makes larger power calculations easier to understand.

Watts vs kW

Both measurements describe usable electrical power.

If startup requirements are ignored, generators may:

• trip breakers
• struggle to start equipment
• experience voltage drops
• become overloaded

This is why generator sizing should always consider both running and startup loads.

How kVA, kW, Amps And Watts Work Together

Although these electrical measurements are different, they all describe the same power system from different perspectives.

Think of it like this:

• kVA tells you the total generator capacity.
• kW tells you how much usable power is available.
• Watts tell you how much power equipment requires.
• Amps tell you how much electrical current is flowing.

Understanding all four measurements makes generator sizing significantly more accurate.

Generator Sizing Example

Imagine a food truck requires:

• Refrigerator = 700W
• Coffee machine = 2,000W
• Lighting = 300W
• Water pump = 500W

Total running load:

3,500 watts

Or:

3.5kW

After allowing for startup loads and future expansion, a generator specialist may recommend a 5–10kVA generator depending on the equipment being used.

This provides enough capacity for reliable operation without overloading the generator.

Common Generator Power Calculation Mistakes

Ignoring Startup Loads

Startup loads can be several times higher than running loads.

Using Only Appliance Labels

Equipment labels often show running power but not startup demand.

Forgetting Power Factor

Commercial and industrial equipment may have varying power factors that affect generator sizing.

Choosing The Cheapest Generator

An undersized generator often costs more in downtime, maintenance, and fuel inefficiency.

Not Allowing For Future Growth

Many businesses add equipment over time. Leaving some spare generator capacity can prevent costly upgrades later.

Frequently Asked Questions

What is the difference between kVA and kW?

kVA measures apparent power, while kW measures usable working power. Most diesel generators operate using a power factor of 0.8, meaning a 100kVA generator typically produces around 80kW of usable power.

Why are generators rated in kVA?

Generators are rated in kVA because electrical loads can vary depending on power factor. Using kVA provides a more accurate representation of total generator capacity.

How many amps does a 100kVA generator produce?

A 100kVA generator typically produces around 417 amps single phase or approximately 139 amps per phase on a 3 phase system, depending on voltage and configuration.

Is kW the same as watts?

Yes. One kilowatt equals 1,000 watts.

Which measurement is most important when sizing a generator?

All measurements matter. Generator sizing typically starts with kVA, but kW, amps, running loads, and startup loads should all be considered when selecting the correct generator.

Conclusion

Understanding the difference between kVA, kW, amps, and watts makes generator sizing far easier and helps prevent costly mistakes.

While kVA measures total generator capacity, kW and watts represent usable power, and amps indicate electrical current flow throughout the system.

Whether you are powering a construction site, commercial facility, event, food truck, or backup power system, understanding these measurements helps ensure your generator is correctly sized, operates efficiently, and delivers reliable performance.

If you're unsure what size generator you need, SGH can help calculate your power requirements and recommend the right solution for your application.

Need Help Choosing The Right Generator?

Contact SGH today for expert advice on generator sizing, temporary power solutions, generator hire, and commercial backup power systems.

Whether you need power for a construction site, event, food truck, commercial facility, or emergency backup application, our team can help you calculate your requirements and recommend the right generator for the job.