• FREE Delivery Mainland UK
  • NO Hidden Fees / All Prices include VAT
  • Expert Advice & After Sales

What Size Generator Do I Need?

Determining the right size generator for your needs can be difficult. Too small, and you risk not being able to power your devices or damaging your generator; too large, and you may end up spending more than you need to. For the most part, determining the appropriate generator size depends on the specific items you intend to power, but there are several other factors to consider. In this article, we’ll explain why generator size is important, how generator size is determined, and what factors you should consider when choosing a generator to help you make an informed decision about the right size generator for you.

Why Generator Size Matters

Having a generator with sufficient power is important for several reasons, including but not limited to:

  1. Safety: Running high-wattage appliances with a generator that is too small can lead to generator overload, causing damage to your appliances or the generator itself.
  2. Energy Efficiency: An oversized generator may not operate efficiently at low loads, resulting in wasted fuel and increased maintenance costs.
  3. Cost Effectiveness: Oversized generators come with higher upfront costs, installation expenses, and fuel consumption, and undersized generators will require frequent repairs or replacements due to overloads (increasing long-term costs).
  4. Performance: An appropriate generator will handle all the essential requirements of your building and its appliances, ensuring a consistent and reliable power during outages. If you purchase an undersized generator, on the other hand, you run the risk of poor performance or running out of power.

How Generator Size Works

To calculate the appropriate size of generator required to power your home or business, you should first understand the factors that influence generator size.

Wattage (W) and Kilowattage (kW)

Generators are rated by their power output, which is measured in watts (W) or kilowatts (kW). Watts represent the amount of electrical power produced, while kilowatts are equivalent to 1,000 watts.

Starting (Surge) Wattage vs. Running (Continuous) Wattage

Running watts is the amount of continuous power needed to keep items running. Starting watts, on the other hand, refers to the extra power a generator must provide to turn on an appliance. Running and starting watts requirements differ for every appliance, and some appliances require no surge power (starting watts) to turn on.

You need to consider both the starting and running wattage of all the devices you intend to power to ensure your generator can handle both.

Load Size

Load size refers to the appliances and devices that you need to power. Before you choose a generator, you need to determine the appliances and devices that you want to power and, if you’re planning to use a generator for emergencies, the devices that ensure critical functions remain operational.

For example, if you’re looking to power your home, you will want a generator that can keep your lights, refrigerator, kettle, oven and internet on in the case of an outage. In a hospital or medical centre, you’ll need a much larger generator that keeps lights turned on and machines and refrigerators working for an extended period of time.

For camping or a construction site, on the other hand, you’ll often just need a portable generator that powers your essential tools, appliances and lights.

Factors to Consider When Choosing a Generator

Now that we’ve covered the basics, here’s the factors you should use to determine the right generator size for your needs:

1. Appliances & Wattage

The size of your generator will depend on what you hope to run, for example, during a power outage. Create a list of all the appliances and devices you’ll need to power during an outage and their approximate starting and running wattage. Add up the starting and running wattage requirements for all the appliances and devices on your list. This total represents the minimum wattage capacity your generator should provide to meet your needs.

If you’re powering a house, you can assess the power requirements of the distribution board in your house, which tends to operate at a voltage of 230V and has a capacity of 100 Amps. Covering this power demand would require a generator with a capacity of 23kW (230V x 100A = 23,000W = 23kW), which can supply electricity to the entire house.

However, if you’re planning to power specific items, such as the lights, fridge, kettle and internet, you can estimate the power consumption per device. You can find the individual wattages of an item on the equipment itself, in the user manual, on a manufacturer’s website, or by contacting the manufacturer.

A power calculator can also help with this step, by determining the continuous power rating you require when you add up all of your essential devices. To help you get started, here’s an idea of the starting and running watts of typical household appliances:

Appliance Wattage (Running) Wattage (Starting)
Refrigerator 1200 200
Freezer (Chest) 1600 400
Freezer (Upright) 2200 500
Microwave (1000W) 1000 1000
Toaster (2-Slice, 1000W) 1000 1000
Dishwasher (1200W) 1200 1200
Washing Machine 2400 1200
Space Heater (1500W) 1500 1500
Television (LCD, 42″) 120 120
Computer (Desktop) 300 300
Laptop 250 250
Ceiling Fan 60 60
Light Bulb (LED) 10
Light Bulb (Incandescent) 60
WiFi Router 20 20

Choosing a generator with more than the minimum required is advised to avoid overloading, and to accommodate for any future growth in the number of appliances that require power or changes in your usage patterns. Indeed, most generators can sustain only 80% of their maximum power for an extended period. If you continuously operate your generator at over 80%, you risk damaging the generator and its appliances. Thus, although you shouldn’t choose a generator that’s too large, one that is slightly more powerful than required is a good idea.

2. Generator Type

Generators can be categorised into several types based on their design and intended use:

  • Standby Generators: Standby generators are installed outside your home or business, and often automatically turn on during a power outage. These can power your entire building for an extended period of time.
  • Portable: Portable generators are ideal for camping, outdoor events, or powering a few essential appliances during a power outage.
  • Inverter Generators: Inverter generators are lightweight, portable and quiet generators that are suitable for recreational activities and powering or recharging battery-operated devices.

A large industrial standby generator, run with natural gas.

3. Physical Size

Generators come in various sizes and configurations, ranging from portable units suitable for camping or small residential use, to large standby generators designed for powering entire homes or commercial buildings. Consider the available space for installation and storage when selecting the physical size of your generator. The ideal outcome is that you have a generator that fits in your space and meets your power requirements.

4. Noise Level

Large generators tend to be louder, while smaller (or inverter) generators tend to be quieter. If you’re powering a loud site, noisy generators might not be a problem. However, if you plan to use them in an area with noise restrictions, you may need a quieter model, such as a silent generator.

5. Frequency of Power Outages

Homeowners living in areas that frequently experience power outages will need a reliable generator that can immediately power their homes during a power outage. Meanwhile, those who don’t experience regular power outages or require a generator for recreational purposes, can opt for a portable or mid-sized unit.


Selecting the right size generator is crucial for ensuring that your essential appliances and devices remain powered, including during emergencies. By following the steps outlined in this guide, you can calculate your wattage requirements and choose a generator that meets those needs.

Looking for a quality generator? At Generators Direct, we offer a range of generators, power stations and power banks for your specific needs. All of our products are manufactured, tested and certified to industry standards, and come with a price promise – you won’t find prices cheaper anywhere on the web, but if you do, we’ll match them. In addition to this, all orders come with free mainland UK shipping and after sales support from our experts.

If you require additional advice or have a question for our team, don’t hesitate to get in contact with us using this form or via phone at +441639849847.