Running Watts vs Starting Watts: The #1 Generator Sizing Mistake

The Most Common Mistake in Backup Power

When people buy a generator, they usually add up the wattage of the devices they want to run. Fridge (700W) + Window AC (1000W) + Lights (100W) = 1800W. They buy a 2000W generator, plug everything in, and the generator immediately trips its breaker and shuts down.

Why? Because they forgot to account for Starting Watts.

What Are Running Watts (Rated Watts)?

Running watts, also known as rated watts or continuous watts, is the amount of power an appliance needs to continuously operate once it is already turned on and running smoothly. This is the baseline power draw.

What Are Starting Watts (Surge Watts)?

Starting watts is the brief burst of extra power required to get an electric motor moving from a dead stop. This surge typically lasts for just 1 to 3 seconds.

Think of it like pushing a heavy car in neutral. It takes a massive amount of physical effort (surge) to get the car rolling. But once it's moving, it only takes a little bit of steady effort (running) to keep it rolling.

Which Appliances Have Starting Watts?

Any appliance with an electric motor or a compressor will require starting watts. This includes:

• Refrigerators and Freezers
• Air Conditioners (Window, RV, Central)
• Well Pumps and Sump Pumps
• Air Compressors and Power Saws
• Washing Machines

Appliances with resistive heating elements (like space heaters, toasters, or coffee makers) or electronics (TVs, laptops) do not have starting watts. Their running watts and starting watts are identical.

How to Calculate Your True Generator Need

You only need to add the highest starting wattage to your total, because you should never start all your heavy appliances at the exact same time.

Item	Running Watts	Starting Watts
Well Pump	1000W	3000W (Highest)
Fridge	700W	2200W
Lights	100W	100W

Your calculation: 3000W (Well Pump Surge) + 1000W (Well Pump Run) + 700W (Fridge) + 100W (Lights) = 4800 Watts Total Needed.