Generator Sizing Guide

Choosing the right size generator is often a confusing task that can leave many of us feeling overwhelmed and uncertain. ‘What size generator do I need?’ is the most common question when people are looking to buy one. After all, selecting the wrong size could mean wasting time and money on something that either falls short of our power needs or far exceeds them. Don’t worry, we’ve put together useful and much-needed information to guide you in sizing the correct generator.

This guidance is tailored to ensure you’ll find peace of mind knowing that you’ve chosen the right generator for your unique situation, whether it’s for your home, business, or a weekend getaway.

How do I calculate my Power Needs?

When choosing the right generator, here are 4 things to check:

1 List Applications Needing Generator Power

It’s essential to include both starting and running wattage for each item. Starting wattage refers to the initial surge of power required to start an appliance, often higher than the running wattage. This information can typically be found in the owner’s manual or on an information plate on the equipment. Additionally, gathering the continuous and peak power information for all appliances is crucial to understanding the overall power needs.

2 Convert Power Information to Watts

A calculator may be used to convert power information to Watts if necessary. The conversion depends on the type of load, with Wattage = amps x volts for resistive loads and Wattage = amps x volts x load factor for reactive loads.

In simple terms:

  • Watts: The real power used by something (like a light bulb).
  • kVA: A measurement that includes both the real power (Watts) and some other power that doesn’t do actual work.
  • Amps: This is like the flow of electricity.

If you know the kVA and want to find out the Watts, you need to consider something called the “power factor,” which tells you how efficiently the power is used.

So, to get from kVA to Watts, you multiply the kVA by the power factor and then by 1000. If you know the Amps and Volts, you can also figure out the kVA.

These numbers help you understand how much electricity something needs and help you make sure you have the right equipment to power it.

3 Calculate Combined Power Requirements

When planning to run multiple appliances at the same time, such as a bar fridge, toaster, TV, and portable fan, you need to sum their power requirements, resulting in 920W in this example. Then, identify the appliance with the highest starting power, the bar fridge at 600W, and add that to the total, leading to 1520W. If no devices with electric motors are included, simply sum the running power of all items.

A generator with at least 1520W of continuous power is needed to run these appliances simultaneously. However, choosing a generator with more than the minimum required is advised to avoid overloading and ensure that the appliances can be started or run when needed.

4 Consider the 80% Rule

When selecting and using a generator, it’s important to take into consideration that most generators can sustain only 80% of their maximum power for an extended period. If you continuously operate your generator at over 80% of its capacity, you risk shortening its lifespan and potentially damaging its appliances. Therefore, while it’s essential not to choose a generator that’s too large for your needs, it’s wise to select one that’s slightly more powerful than required. This will provide a buffer, ensuring that you don’t push the generator too hard, preserving its life and protecting your connected devices.

What size generator do I need?

WattsPower CategoryTools Appliances
5000WBasic power system
  • Lights, fans, sump pump, and refrigerator/freezer
6500WSmall power system
  • Lights, fan, sump pump, and refrigerator/freezer
  • Television, entertainment system and heating/cooling system
8000kWA mid-sized power system
  • Lights, fan, sump pump, and refrigerator/freezer
  • Television, entertainment system and heating/cooling system
  • Home office
10,000W and 12,000WAn emergency backup power system
  • Lights, fan, sump pump, and refrigerator/freezer
  • Television, entertainment system and heating/cooling system
  • Home office
  • Kitchen
  • Total about 100 Amps
15,000 WA powerful system to run a small home
  • Lights, fan, sump pump, and refrigerator/freezer
  • Television, entertainment system and heating/cooling system
  • Home office
  • Kitchen
  • Laundry room
  • Total about 150 Amps
25,000WA mini-power plant that can run a small to mid-sized home or business.
  • Lights, fan, sump pump, and refrigerator/freezer
  • Television, entertainment system and heating/cooling system
  • Home office
  • Kitchen
  • Laundry room
  • Air conditioning system
  • Total about 200 Amps
30,000W and upA mini-power plant that can run a mid-sized to large home or business.
  • All of the above and more. Live in total comfort.

Generator Size Classification in kVA

kVATools Appliances
10 kVA GeneratorOffering substantial power, suitable for running multiple appliances and devices simultaneously. Ideal for larger homes and businesses.
3.5 kVA GeneratorA versatile option, capable of powering essential appliances in a residential setting. Perfect for backup power during emergencies.
20 kVA GeneratorIt provides robust power output, making it an excellent choice for comprehensive residential backup or smaller commercial applications.

Navigating Portable and Standby Generators for Seamless Power Solutions

When it comes to emergency power, portable generators are a popular choice for their versatility and ease of use. Experts recommend a minimum generator size of 5,000 watts for home emergency use, ensuring you have enough power to keep your essential appliances running smoothly. However, it’s important to note that quality plays a significant role in generator pricing. While cheaper options might be tempting, investing in a high-quality portable generator ensures reliability and longevity, which is crucial during critical times. If you’re wondering what size generator for a house in Australia is appropriate, considering the unique power needs of your location and the appliances you want to run will guide you toward the optimal choice.

One essential safety tip is never to run portable generators indoors. Carbon monoxide poisoning is a real and deadly risk when generators are used in enclosed spaces. To safely use a portable generator, you’ll need appropriate extension cords that are rated for the load you intend to connect. These cords ensure efficient power delivery while maintaining safety standards.

Home standby generators are ideal for those seeking a more comprehensive power solution. These systems provide seamless power to your entire home through an automatic transfer switch. Designed to activate within seconds of a power outage, they offer uninterrupted electricity, regardless of whether you’re at home or away.

It can be fueled by natural gas, propane, or diesel fuel, offering flexibility to suit your preferences and local availability. Their installation takes place outdoors, similar to a central air conditioner, eliminating the need for manual intervention in inclement weather.

Furthermore, these generators are well-suited for critical applications such as life support equipment and computers. Incorporating an uninterruptible power supply (UPS), essentially a battery backup, ensures that sensitive devices remain powered during the transition to generator power.

Essential Guide for Portable Generator Sizing

Use the chart below to determine your usage requirements for a portable generator.
Values are an estimate for reference only.

DeviceRunning WattsStarting Watts
Air Condition – 1 HP7501500
Fridge (Small)300600
Colour TV – 20″250250
*Some equipment like an air-condition system will require double the rated wattage to run. Refer to starting watts in chart
*When camping, try to avoid heating products such as: kettles and coffee machines, as they draws lots power. Try using portable gas appliance
DeviceRunning WattsStarting Watts
(Medium) Refrigerator/Freezer5001000
Sump Pump 1/2 HP375750
DeviceRunning WattsStarting Watts
Radio/CD/DVD Players50-20050-200
Inflator Pump5050
Electric Grill16501650
Box Fan200200
Outdoor Light String250250
Icecream Truck5000-80005000-8000
Coffee Van5000-80005000-8000
DeviceRunning WattsStarting Watts
Light Bulbs – 60-70 Watt7070
Well Pump5001000
(Medium) Refrigerator/Freezer350700
Microwave – 750 Watts750950
Coffee Maker10001000
Electric Stove -6° Element16001600
Colour TV-27″350350
Security System350350
Computer with 17″ Monitor450450
1/2 HP Garage Door450900
Sump Pump 1/2 HP*5001000
Washing Machine7501500
*Some equipment like an air-condition system will require double the rated wattage to run. Refer to starting watts in chart
DeviceRunning WattsStarting Watts
Power Hand Drill700700
Belt Sander – 3*10001000
Air Compressor – 1/4 HP185400
Air Compressor – 1 HP7501500
Air Compressor – 2 HP15003000
Table Saw20002000
LED Flood Light200200
Reciprocating Saw960960
Circular Saw-71/4″10001000
Battery Charger300300
Cement Mixer5501100
Welder 140Amp44004400
Grinder 5*10001000
Grinder 923002300
Drop Saw 1018001800
Shop Vac11001100
Jig Saw600600
Jack Hammer (Large 16KG)18001800
Jack Hammer (Medium 6KG)11001100

By following these guidelines, you’ll have peace of mind, knowing you’ve chosen the right generator for your unique situation.