What size generator do I need? The fact that you're asking this question means you're off to a good start! Generators vary in size, from 1800-watt units all the way up to whole-house generators capable of producing 20,000 watts or more. With prices varying widely, it can be a challenge to get what you want without spending more than you should. After all, the best generators can be any size. It all depends on your needs.
For the sake of argument, let's focus on buying a portable generator. After all, we're a power tools website dedicated to building. However, what is good for the job site often also applies to emergency power. With this in mind, let's take a closer look at the question of what size generator you should buy.
In general, we find that generators fall into a few key classes. This can help you narrow it down right away. Manufacturers make generators in many sizes. They vary in power output, or wattage level. The following "breakpoints" are a good starting point when sizing generators.
Quick Tip: Generators have a starting wattage and a running wattage rating. Some brands advertise starting wattages. Others emphasize operating power. Running watts tells you what the generator can consistently deliver. Startup wattage only affects the power available the first time you start up.
Generators under 2000 watts
Under 2000 Watt Generator sizes and ratings you'll find the best prices and smallest units. Most of these smaller models run on gasoline. However, some battery-powered generators can be charged using solar panels. These seem to work best for tailgating and camping. For emergency power, the lower output wattage limits you to lights, fans, and possibly a small refrigerator or other appliances. These smaller generators probably won't give you the power you need to run 15 amp tools on the job site.
2000 watt generator
Once it hits around 2,000 watts, the generator starts handling power tools and as a short-term fix for power-starved worksites. Don't get us wrong—we love a compact 2,000-watt generator for camping, too. However, going to higher power levels allows you to handle more field applications. Small angle grinders, sanders, jigsaws, etc. We've seen people run small miter and table saws on lower output generators, but we generally don't recommend this. Stick to the larger units for serious jobsite use.
For us, the 2000 watt generator comes down to flexibility and value. These small units are extremely portable, and they can be used in both camping and select job sites. This makes them one of the most versatile generator sizes you can buy.
5000 watt generator
Use a 5000 watt size generator for the level of power you're most likely to find on the job site. It's great for running multiple power tools. This includes those heavy duty 15 amp table saws and miter saws. When it comes to emergency power, you can run your refrigerator with lights, fans, or even window air conditioners. If you have your own water pump, this is the smallest you should consider. Just make sure you get one with a 240V plug.
7500 watt generator
At a generator size and rating of 7500 watts, you start to lose some of the portability. You can still roll it, but in many cases you're over 200 lbs. Those extra 2000 watts allow you to run virtually your entire jobsite without power. You can run lights and fans as well as multiple power tools at the same time. You'll usually find a 240V plug as standard equipment on these units.
These generators are also starting to branch out into the types that can provide you with emergency power in your home in a pinch. We love using these generators after a hurricane.
10,000 watt generator
A 10,000 watt generator is pretty much the size and class of portable generators. In addition to this, you will also come across stationary products. If you have the strength to move it, you can power a larger residential workplace or even a small house. It's tempting to wire a unit of this size directly into your breaker. Just make sure there is a qualified electrician doing the job. The consequences of miswiring can be disastrous.
What generator size do I need? let's talk real numbers
To specifically answer the question "What size generator do I need?", you need to look at your specific situation. As you know, everyone is at least a little bit different. For Construction Pro, let's look at which tools and products you typically operate. The process is simple. Only the watts needed to run everything at once, and include the starting watts for the max power draw tool. Let's say you have a miter, table, and circular saw, and a battery charger for your cordless tools.
Calculate potential load
- Miter Saw: 1800 Running Watts, 3400 Starting Watts
- Table saw: 1800 watts. 3500 starting watts
- Circular Saw: 1800 Running Watts, 3200 Starting Watts
- Power Tool Battery Charger: 330W
It takes 5,730 watts to run all tools at once. Also, your table saw has its greatest starting needs at 3500 watt hours. With that in mind, you need to increase the requirement by 1700 watts to 7430. This means you need a generator that runs at least 7500 watts. If you and your team are serious about using one tool at a time, you can drop that down to a 4000-watt unit.
Closing the Generator Sizing Discussion
As you can see, the demand for more electricity rises rapidly. It's always important to start with the question: "What do I really need to run?" Using less generator power is one of the things that makes cordless tools so attractive. Consider this – we have a solid selection of cordless miter and circular saws. Just by upgrading some tools to be cordless, your generator needs could drop by around 4000 watts.
You can use the same formula to decide what size generator you need to buy for emergency power situations. Remember the difference between needs and wants!