What Size Generator Do I Need to Run Power Tools on a Job Site?
Look, I’ve been behind the hire counter for 12 years now. I’ve seen it all: from the young apprentice who tries to run a 2000W welder off a camping inverter, to the site foreman wondering why his drop saw trips the breaker every time he hits a knot in the timber. Choosing the right generator isn't just about grabbing the biggest unit on the lot; it’s about understanding the delicate dance between starting watts and running watts.
Whether you are prepping for a backyard renovation or you are managing a busy construction site, temporary power is the backbone of your productivity. If you get it wrong, you’re either wasting money on fuel and transport, or you’re standing around waiting for the generator to reset while your team stares at their watch. Let’s break down exactly how to size your gear like a pro.
Understanding the Basics: Starting Watts vs. Running Watts
Before you even look at the power rating, you need to understand the "surge." Most power tools—especially those with electric motors like grinders, circular saws, and compressors—require a massive burst of energy to get the motor spinning from a dead stop. This is your starting wattage.
Once that tool is up to speed, it settles into a lower power consumption level. That’s your running wattage. When you are looking at your generator wattage for tools, you must size for the starting watts of your most power-hungry device. If you don't, the generator’s internal circuit protection will simply cut the power to protect the alternator.
The Golden Rule of Sizing
Always add 20% to your total calculated demand. You never want to run a generator at 100% capacity for 8 hours a day. It kills the engine, chews through fuel, and limits the lifespan of your machine. When you consult with experts like those at Wenbro Hire, they’ll tell you the running watts vs starting watts explained same thing: overhead is your best friend.
Worksite Tool Wattage Reference Table
To help you plan your worksite temporary power requirements, I’ve put together this quick-reference guide based on standard tool ratings. Keep in mind, these are estimates—always check the compliance plate on your specific tool.

Tool Running Watts (Approx.) Starting Watts (Surge) Corded Drill (10mm) 500W 750W Circular Saw (185mm) 1,400W 2,300W Angle Grinder (125mm) 1,200W 2,000W Air Compressor (Small) 1,500W 3,500W Hammer Drill 1,000W 1,500W Work Lights (LED) 100W 100W
Matching the Generator Type to the Job
Not all generators are created equal. In my experience, choosing the wrong "flavour" of generator is where most blokes get unstuck.
Inverter Generators: These are the quiet ones. They produce "clean" power, which is essential if you are charging sensitive electronics, laptops, or using tools with digital controllers. They are lighter and more fuel-efficient, but they usually max out at around 3kVA to 5kVA. Perfect for fit-outs and smaller jobs. Frame-Style (Open Frame) Generators: These are your workhorses. They are loud, rugged, and built to handle the constant vibration and dust of a demolition or framing site. If you have multiple blokes running heavy-duty gear, this is what you want. Diesel Generators: If you are on a long-term site, go diesel. While the initial hire cost is higher, the fuel consumption is significantly lower, and they are built to run for 12+ hours straight without a hiccup.
Fuel Choice and Daily Run-Time Planning
When planning your site power, look at your workday. If you are only using tools for two hours a day, a small portable petrol unit is fine. If you are running multiple crew members from 7:00 AM to 4:00 PM, you need a larger fuel tank.
A common rookie mistake is running the tank dry while a tool is under load. This can cause a voltage drop as the engine chokes, which is a great way to fry the motor of an expensive tool. Always ensure the generator has a fuel gauge and that you have a documented schedule for refuelling—never refuel while the engine is hot and running.
Noise and Local Considerations
In Australia, we have strict rules about noise pollution, especially in residential zones. You cannot just rock up to a suburban reno and fire up a massive, loud industrial open-frame generator at 7:00 AM. You will have the local council knocking on your door by 8:30 AM.
The Australian Government Department of Climate Change, Energy, the Environment and Water provides guidelines on environmental standards, and local councils have specific decibel limits for residential construction. If you are working generator rental in a quiet neighbourhood, hire an inverter unit or invest in acoustic sound blankets to baffle the noise. Being a good neighbour keeps your project running smoothly.
Got Questions? Let’s Talk.
I know the math can get tricky, especially when you start adding up multiple tools running at the same time. If you look at the bottom right of your screen, you'll see our Chatlio integration bubble. Let me tell you about a situation I encountered made a mistake that cost them thousands.. That isn't a bot—it’s actually me or one of the boys from the counter. If you aren't sure if your generator can handle that heavy-duty masonry saw, just hit us up and send us the specs.
Share Your Experience
Have you ever had a generator die on you in the middle of a pour? Or do you have a favourite brand that’s survived a decade of abuse on the tools? Let us know in the comments below!

Spread the word:
Share on Facebook Tweet this guide Pin to Pinterest Post to LinkedIn Share on Tumblr Schedule via Buffer
Leave a Comment
Please login to post a comment or ask a specific question about your site requirements.