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What Size Generator Do I Need?

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Diesel generators are investments that will last years, supplying power to your business or home. When purchasing a generator, you’ll need to consider numerous things, including its main purpose, where you’ll use it and – most importantly – which size you’ll need.

Spending money on a powerful generator is a good idea, but it depends on what you’ll use it for. In contrast, opting for small generators might not meet the power requirements of your home or business.

To ensure you know which size generator to choose, we’ve put together this helpful guide.

What do I need to consider when purchasing a generator?

Diesel generators come in various sizes, but you can also select models based on your needs. Understanding what you’ll be using the generator for can help you when it comes to choosing the right size, power type and model.

The types of generators available include: 

  • Prime Generators: These generators are favoured for off-grid operations and powering large events. Industrial generators typically deliver a lot of power and are more expensive.
  • Standby Generators: Homes and businesses invest in standby generators for protection during a power outage. These generators come with automatic transfer switches, ensuring a seamless transition when you lose access to your main electricity supply.
  • Portable Generators: If you’re working on a smaller construction site and need to use power tools or going on a camping trip, portable generators can supply reliable power. However, they’re only for temporary usage and can lack the performance of prime and standby generators.
  • Inverter Generators: These generators are similar to portable models, but their unique design enables them to power TVs, computers, and phones without damaging them.

AC or DC?

Aside from deciding on the type of generator, you’ll also need to consider whether AC or DC power options:

  • AC power is the type of power that most appliances and electronics use.
  • DC power is typically used for engine starters, welding machines, and other industrial equipment.

If you’re not sure what type of power your devices use, check the owner’s manual or look for a label on the device itself.

Does size matter?

The size of a generator is an important consideration, especially when it can mean the difference between an emergency power outage, powering an entire house, or simply running a couple of electrical devices.

To size a generator, consider the power you’ll need to run your appliances and electric equipment.

A small generator may be enough to power a few essentials, like electrical tools. A larger generator may be necessary if you’re running larger appliances or multiple home appliances at once. 

You should also consider how long you’ll need to run the generator; a fuel tank may only last a few hours, so you’ll need to refuel regularly if you’re using it for extended periods.

Ultimately, what size generator you’ll need depends on your specific needs.

A selection of large standby generators

Diesel generators for prime power

Prime power generators are designed to provide seamless electricity for a range of applications. Whether you’re working on a large construction site, powering electrical equipment or need power for an event, these diesel generators offer an uninterrupted supply and won’t disrupt your operations.

Even though you’ll be using the generator for prime power, there are still important considerations.

How often will you be using it?

Will you be using the generator for hours at a time? Or is it to power construction operations as and when needed?

If you live in an area with frequent severe weather, it’s a good idea to choose a generator that can run for at least 24 hours on a full tank of fuel.

Where will the generator be used?

Whether you’re using a portable generator on a construction site or regularly working in an off-grid location, you’ll want to ensure the model you choose can fulfil your power requirements.

For example, small-scale constructions and electrical appliances require a lower power output than using a generator for a large festival.

Standby generators for homes

standby generator is a great way to ensure your home has power during a power cut. But how do you determine the size of the backup generator you need to run and power your entire house?

The answer depends on several factors, including the size of your home, the number of appliances you want to run, the number of devices you want to power, and the overall amount of power you need.

How large is your home?

The size of your home matters, as it defines how much power you’ll require. For example, a small home might only need a 5,000-watt generator. But if you have a large home or want to run multiple appliances, you might need a 10,000-watt generator or more.

It’s crucial to figure out the right size generator for your home because a small generator could leave you without adequate power to run your home when needed.

It’s also important to know your home’s specific backup power needs so that when you use your generator, it doesn’t overload and short out, leaving you without power completely.

How to choose the right size home standby generator

To size a standby generator, start by calculating the wattage of the appliances you want to power. Then, add the wattage of all the appliances you want to run simultaneously.

Here’s how to make the job easy: 

  1. List all the devices and appliances you want to run, for example, a refrigerator, air conditioning units, washing machines, and security systems.
  2. Note down the starting wattage (this is what it needs to start up), followed by the running wattage they need (what it needs to run after start up). These figures are important for determining the size you need for your home.
  3. Choose a standby generator size to cover the total wattage you need. If your generator is only big enough to generate power for the running watts but not the starting wattage, your generator might short.
  4. Consider getting a generator slightly bigger than your needs. The generator size should reflect your home’s specific backup needs, plus a little extra so you have power for all your appliances without worrying about the generator overloading.

Of course, a larger generator, such as a whole-house generator, will be more expensive than a smaller one, but it will provide more peace of mind during an outage.

Standby generators for business and commercial applications

Many businesses invest in standby generators to supply power during an outage. These generators provide vital support, ensuring operations can continue and giving customers a seamless experience.

When choosing a generator size for your business, here’s what you should consider.

What is it powering?

If you plan on using a generator to power your business in an outage, it’s important to know which appliances and pieces of equipment you’ll need to power.

During a power outage, portable appliances can be plugged into generators. Common examples include lighting, portable heaters, machinery, and air conditioners.

The size of generator you need will depend on the number and type of equipment you want to run. For example, if you’re powering large machinery or expansive retail stores, you’ll need a generator to handle those loads.

Do you need to power your modern electronics?

Remember to factor in things like lights, electronics, and any other devices you might want to keep running during an outage.

Once you’ve determined what you need to power, choosing the right generator is critical in ensuring your business is prepared for an emergency. This might mean investing in an inverter generator, the best option for sensitive electronics.

Calculating the standby generator size

When calculating the right generator for your business needs, you can follow the same method for a home. However, remember to assess your equipment and choose a generator that meets your requirements.

Standby or portable generator, you do the math!

A rule of thumb is that a portable generator should be able to provide at least 1000 watts for every 100 square feet of space.

A standby generator is an excellent choice if you want the peace of mind that comes with being prepared for a power outage.

But how do you know what size standby generator you need? The first step is to calculate your home’s power usage by adding up the running wattage of all the appliances and devices you’d want to run in an emergency.

Once you have your total, add 1000 watts for starting wattage because most appliances need more power to start up than they do to run.


Figuring out what size generator you need can be a daunting task. With so many factors to consider, how do you know which generator is right for you?

That’s where Solent Power comes in. We have years of experience helping people find the perfect generator for their needs. We understand the importance of finding the right size generator, and we’ll work with you to ensure you get the best product for your money.

Contact us today to learn more about our generators and how we can help you choose the one that best suits your needs.

Paul Phelps Solar Power Owner
Paul Phelps
Paul is the MD of Solent Power and specialises in emergency power solutions, helping to protect your facilities from power loss. Get in touch with us today to discuss the different power brands that we can offer and how they can suit your needs.
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