What Size Generator Is Needed for a Construction Site?

If you're a construction contractor, there's a good chance you'll need to rent a generator at some point. Generators provide electricity for tools, equipment and lighting at remote sites that don't have access to the power grid. They can also provide emergency backup power when an outage occurs, minimizing the risk of costly downtime.

When you're looking for the best job site generator for your construction projects, you'll discover that they come in a wide variety of sizes, configurations and power output capacities. It's important to select a model that provides sufficient power to keep your site running, but not so much that you end up wasting electricity — and money.

Factors to Consider When Selecting a Generator for Construction

As a rule, you'll want a generator that provides enough power for your site when operating at 70-90% capacity. A generator that runs at less than 50% of its capacity creates a situation called "wet stacking," which significantly reduces the unit's operating efficiency.

Taking the following factors into account can help you determine the proper size and output capacity for your generator rental:

  • Site size: As you might guess, the larger the size of your construction site, the more power you'll need your generator to produce. Bigger sites may require several generators to meet the power requirements.
  • Equipment types: If your construction job demands the use of heavy-duty equipment and tools, you'll need a generator with more wattage than when using smaller products that consume less electricity.
  • Reserve power: Some pieces of equipment require more electricity to start up than they do to operate. Make sure you choose a generator that can accommodate power surges that may occur when starting several machines or tools at once.
  • Voltage capacity: Along with a generator's wattage, you should also consider the voltage it can provide. The higher the voltage output, the stronger the electrical current the generator will deliver.
  • Phase: Generators come in single and three-phase options. For a construction project, you'll likely need the latter version, as it will deliver a more stable and reliable power supply.

A simple way to calculate the best job site generator size for you is to add up the wattages of all the equipment and tools that require electrical power. You can then compare this total with the wattage of the generators that are available for rent. Be sure to choose a model that offers a little extra capacity to account for power surges and the possible addition of more equipment during the project.

Use a Generator Sizing Calculator to Simplify the Process

commercial generator sizing calculator gives you an easier way to determine the appropriate size for your units. Start by making a list of all the tools and machinery (air compressors, saws, jackhammers, portable office and computer equipment, etc.) that may require electrical power at your construction sites. You can then check the starting and running wattage for each, which is inscribed on the equipment. 

Finally, calculate your total power requirement by adding all the kW or KVA amounts. The power capacity of the generator you choose should exceed this figure by 10-20% to give you a margin for error.

Diesel vs. Natural Gas Generators

Another factor to consider when choosing a generator for your job site is the fuel source. Both diesel and natural gas-powered models are available, and each offers certain advantages.


Benefits of diesel generators include:

  • Efficiency: While diesel fuel is more expensive than natural gas, it's also more energy-dense. You'll get more out of a unit of diesel than from the same volume of gas.
  • Steady power: Diesel is a reliable energy source, making it an excellent choice for job sites that require a constant, long-term power supply.
  • Sturdy construction: Diesel engines feature a rugged design that can withstand the rigors of heavy use and still provide a long life span.
  • Safety: Diesel is less flammable than many other fuel types. The absence of spark plugs in diesel engines lowers the likelihood of flash fires.


Some advantages offered by natural gas generators include:

  • Clean burning: These days, construction operations must meet increasingly stringent emissions requirements. Natural gas burns more cleanly than other fuel sources, enabling you to stay compliant and be a good steward of the environment.
  • Lower upfront fuel costs: Natural gas is one of the cheapest fuel sources.
  • Efficiency: Like diesel, natural gas is a highly efficient fuel, resulting in low energy costs. 
  • Accessibility: The underground utility lines and infrastructure are already in place to facilitate natural gas delivery, providing easy access at many construction sites. These models often eliminate the cost and hassle of storing a fuel supply.

Get Help Choosing the Right Generator for Construction

The Cat® Rental Store carries an extensive inventory of portable generators for rent at competitive rates. Our fleet features products from Caterpillar, ensuring you get equipment that meets your performance, reliability and quality standards. Units are available in a wide range of sizes to meet any power generation need. Our generator rentals are also towable, enabling you to transport them to and from your sites and place them in the ideal locations.

We also have the expertise to help you select the best job site generator for your power requirements. Our team will work closely with you to calculate your electricity needs based on all the above factors. You'll get the right-sized equipment and receive guidance on how to configure it at your construction site.

Browse Our Generator Lineup Today

The Cat Rental Store can help you explore all the benefits of renting generators and other equipment, such as more fleet flexibility, lower operating costs, immediate availability and better results due to using job-specific models. We also offer flexible terms and a full menu of services to maximize your customer experience.

Feel free to browse our current generator lineup. Give us a call at 1-800-RENT-CAT or check in with your nearest location for more information and tips on choosing a model — we're available around the clock to assist you. To request a fast quote, please fill out and submit our online contact form.

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