Construction Site Generator Sizing: The Full Tool Wattage Chart
Construction site generator sizing goes wrong in one specific way: adding up the starting wattage of every tool on site. That method oversizes the set by a third or more, and an oversized generator runs lightly loaded, wastes fuel, and wet stacks. The correct method is to sum the running wattage of everything operating simultaneously, then add only the largest single starting surge, because two motors almost never start in the same instant.
Power Tool Wattage Chart
| Tool | Starting Watts | Running Watts |
| Circular saw, 7 1/4 inch | 3,000 | 1,500 |
| Worm drive saw | 3,100 | 1,560 |
| Miter saw | 2,100 | 840 |
| Jig saw | 1,800 | 720 |
| Drill | 1,800 | 720 |
| Router | 1,500 | 600 |
| Planer | 2,400 | 960 |
| Orbital sander | 1,800 | 600 |
| Belt sander | 1,000 | 1,000 |
| Disc grinder | 4,000 | 2,000 |
| Concrete cutter, 12 inch | 3,600 | 1,800 |
| Electric chainsaw | 2,400 | 1,200 |
| Paint sprayer | 1,080 | 360 |
| Pressure washer | 3,600 | 1,200 |
| Water pump | 3,000 | 1,000 |
| Air compressor | 4,000 | 2,000 |
| Winch | 5,400 | 1,800 |
Figures are approximate and vary by make, motor type, and condition. Universal motor tools such as drills and sanders draw a modest inrush. Induction motor loads such as compressors, pumps, and winches draw the highest starting current, and those are the items that set the surge allowance. Always size from the tool nameplate where one is available.
Working the Calculation
Take a crew running a circular saw at 1,500 W, a drill at 720 W, an air compressor at 2,000 W, and 1,000 W of site lighting. Running load is 5,220 W. The largest starting surge belongs to the air compressor, at 4,000 W starting against 2,000 W running, so 2,000 W of surge. Peak requirement is 7,220 W.
Generators are rated in kVA, not kW. At 0.8 power factor, 7,220 W becomes 9.03 kVA, so a 10 kVA set covers it with sensible headroom. Adding every starting wattage instead would have returned 9,800 W and pushed the specification a full frame size higher. Our power plant engineering team applies the same logic at station scale.
Two adjustments follow. Ambient temperature and altitude derate the set further, and a site running eight hours a day needs a prime rating rather than standby, which is a lower number on the same machine. Apply both before choosing the frame size, not after.
Frequently Asked Questions
How do I calculate what size generator a construction site needs?
Add the running wattage of every tool that will operate at once, then add the largest single starting surge. Convert to kVA by dividing by the power factor, typically 0.8.
Why not just add up all the starting wattages?
Because motors do not all start simultaneously. Doing so oversizes the set by roughly a third, which raises capital cost and leaves the engine running under light load.
What happens if the generator is too small?
Voltage dips on motor start, tools stall or trip, and the set may shut down on overload. Repeated low voltage operation also shortens the life of the tools themselves.
Does an oversized generator cause problems?
Yes. Diesel generating sets running below roughly 30 percent load accumulate unburnt fuel in the exhaust, known as wet stacking, which fouls injectors and turbochargers.
Correct construction site generator sizing protects both the programme and the plant. USP&E Global has delivered 150+ projects across 35+ countries and holds sets across the full range in our live inventory alongside natural gas options. Energy use and efficiency data is published by the U.S. Energy Information Administration, the U.S. Environmental Protection Agency, and the World Bank.
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