When it comes to generator hire – size matters. It’s important to know roughly how much power your site(s) will need in advance of choosing your generator, as you could bump into a few issues if you under- or overestimate.

You really don’t want to be stuck unable to power your equipment because the generator isn’t powerful enough. Likewise, you don’t want to waste money on something that’s far too powerful.

Whilst you may only require a smaller generator, if it will be used consistently over a long period of time, it could be cheaper to hire a larger generator to avoid constant fuel management.

However, underestimating your power needs could lead to excessive wear and tear on the generator, so be generous when working out your needs – it’s never exact math.

In this blog, we will discuss how you can choose the right generator to meet your site(s) needs.

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Generator Hire: Calculate Your Load Size

Before doing anything else – work out what equipment your generator will be expected to run.

In this stage, make a note of the power requirements of all your equipment and add up the wattage. This will tell you the amount of power you will need on a daily basis, which will tell you the electrical output you will need from your generator hire.

Tip: Remember that some equipment will have a different power requirement on start-up when compared to it’s running wattage. Ensure you calculate the initial surge in wattage from starting up your equipment.

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kW to kVA – Converting Equipment Input To Generator Output

Whilst your equipment’s electrical needs will be calculate in Wattage (kW), generators are rated in kilo-volt-amperes (kVA). kVA measures the apparent power of a system, and electrical systems like generators are never working at 100% efficiency.

International standards generally rate generators as having an effective power factor of 0.8.

It’s hugely important that you bear this in mind when choosing the right generator hire for you. For example: an 150kVA generator, has an actual power factor of 0.8 and therefore will not be big enough to power equipment that needs 150kW of power.

Below is a simple way of converting a generators kVA to KW and vice versa:


Why Should You Calculate Your Power Requirements?

If you’re going to be using the generator as your site(s) main source of power, you’ll need to ensure you calculate for 70-80% capacity.


A generator shouldn’t be ran at maximum capacity for any longer than 30 minutes at a time, in order to avoid problems. Not only will this help maintain stable performance, leaving a healthy 20% safety margin will also leave room for future unforeseen power requirements.

There are a number of issues that can arise if you incorrectly calculate your power needs:

  • System failures on site
  • Overloading the generator
  • Erratic and inconsistent performance
  • System malfunctions due to misuse of equipment

Will The Generator Be A Good Fit For Your Site(s)?

Now that we’ve calculated your electrical load size and the your power requirements, you should be able to easily identify the right size generator to meet those needs. Now it’s time to ask yourself if your site can physically support the generator.

Often this won’t be a huge issue, as there should be plenty of room for the average generator. However, if your site requires a very large generator you should consider site access and ease of manoeuvrability.



We hope these tips help take some of the confusion out of choosing the right sized generator for you.

If you are looking for the right supplier for you, then speak to a team of industry experts that can you can depend on.

At Rehire UK we offer over 10,000 products and a combined 75 years of experience, so you can feel assured that your generator rental will be a simple and efficient experience. Speak to one our team today for any more information.

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