What Size
Generator
Do You Need?
A no-nonsense, Australian-context guide to choosing the right generator for your home, event, construction site or business, without overpaying for capacity you’ll never use, or buying short and frying your gear.
Why Size
Matters
Three failure modes, each one expensive, each one preventable with a single sizing decision made up front.
Too Small
Won’t carry the load. Constant overload trips breakers, stalls equipment and fries alternators within months.
Too Large
Burns extra fuel, costs more upfront, and risks “wet stacking”, diesel buildup that wrecks engines run too lightly.
Wrong Phase or Fuel
Single-phase unit on a three-phase site. Petrol where diesel was needed. Mismatched specs cripple uptime and resale value.
kW vs kVA
– The Difference
Generators are rated in kVA. Appliances pull kW. You need to speak both languages.
The actual usable power doing real work, heating, lighting, motors turning. This is what your appliances consume.
The total power capacity the generator must deliver, including the reactive power lost to inductive loads like motors and compressors.
Single Phase
vs Three Phase
Get this wrong and your generator can’t even connect. Most Australian homes are single phase, most worksites and factories are three phase.
Single Phase
- Most homes, small offices and shops
- Lighting, fridges, TVs, small appliances
- Power tools up to ~2.5 kW
- Generators typically 2 – 20 kVA
Three Phase
- Construction sites, factories, large commercial
- Big motors, pumps, compressors, lifts
- Required for high-load equipment
- Generators typically 10 kVA and up
Power Needs
By Application
Real-world wattage ranges across the four jobs we size for most. Use these as a starting point, then run your own load list.
Home Backup
- Lights & power points0.1 – 0.5 kW
- Refrigerator / Freezer0.5 – 1.0 kW
- Split-system AC2.0 – 5.0 kW
- Microwave / Kettle1.0 – 2.4 kW
Events
- Sound / PA system1 – 3 kW
- Stage & venue lighting1 – 4 kW
- Food trucks / catering2 – 5 kW
- Coolrooms / refrigeration3 – 8 kW
Construction Sites
- Power tools (combined)2 – 10 kW
- Compressors / welders5 – 15 kW
- Concrete mixers / pumps5 – 20 kW
- Site lighting & amenities2 – 6 kW
Commercial / Industrial
- Office floor (per 200m²)10 – 25 kW
- Retail / hospitality15 – 50 kW
- Light manufacturing50 – 150 kW
- Heavy industry / data150 – 500+ kW
3 Steps To
Find Your Size
A repeatable method that works for any application, from a single ute to a 12-storey commercial fitout.
List Every Load
Walk the site. Write down every piece of equipment that will run on the generator, including standby items.
Sum Running Watts
Add up the running wattage of every item you listed. Convert anything in amps using kW = (V × A) ÷ 1000.
Add 20–30% Buffer
Headroom for surge loads, hot weather and the load you forgot. Then divide by 0.8 to convert to kVA.
Starting Power
Is Bigger.
Motors, compressors and pumps draw 2–7× their running wattage at startup, for a few seconds. Miss this and your generator stalls when the AC kicks on.
Same appliance. Two numbers.
A 2 kW air conditioner doesn’t just need 2 kW. The compressor surge can spike to 5 kW for a few seconds, every time it cycles.
Typical Startup Multipliers
| Equipment | × |
|---|---|
| Air conditioner | 3× |
| Refrigerator / freezer | 3× |
| Submersible pump | 4× |
| Air compressor | 5× |
| Heavy-duty motor | 6× |
| Lights / electronics | 1× |
Costly Mistakes
We See Weekly
After 30+ years sizing generators across Victoria, these are the four mistakes that come back to bite buyers most often.
Ignoring startup surge
Sizing for running watts only. The first motor start trips the breaker.
No safety buffer
Running a generator at 100% capacity 24/7 halves its operating life.
Buying on price alone
The cheapest unit is rarely the cheapest over 5 years of fuel and service.
Skipping the expert call
Wrong phase, wrong fuel, wrong enclosure, all avoidable in a 10-minute conversation.
Quick Size
Reference
A pocket-sized lookup. Find your use case, find your range. Then call us to confirm the right model.
| Use Case | Typical Equipment | Generator Size |
|---|---|---|
| Small home / unit | Lights, fridge, TV, basic tools | 3 – 5 kVA |
| Large home backup | Whole-of-home incl. AC | 5 – 10 kVA |
| Events & functions | PA, lighting, food vans | 10 – 20 kVA |
| Construction sites | Tools, compressors, site sheds | 20 – 100 kVA |
| Commercial buildings | Offices, retail, hospitality | 50 – 250 kVA |
| Industrial / data | Factories, plants, server halls | 100+ kVA |
Fuel Type
Matters Too
Once size is settled, fuel choice decides operating cost, runtime, noise and where you can park it.
Most efficient at heavy loads. Long runtime, robust, lower fire risk. The default for everything 10 kVA+ in Australia.
Cheaper upfront, lighter, easier to start cold. Best for < 8 kVA portables and short-duration backup.
Cleaner burning, quieter, and connected to mains gas means no fuel logistics. Popular for permanent commercial standby.
Talk To A Real Person.
East Coast Generators has been sizing power solutions for Australian homes, events, construction and industrial sites since 1990. Get a tailored recommendation, not a sales pitch, in one call.