Buying a generator that is too small leaves you resetting breakers in the dark. Buying one that is too big wastes fuel and money. This free calculator estimates the generator size you need based on what you actually want to run during an outage. Check the appliances you plan to power at the same time, and we will do the math.
Select what you want to run at the same time
This tool gives a practical estimate for planning. Motor-driven appliances briefly draw much more power when they start up, so the calculator adds the largest single starting surge on top of your running total, then applies a safety margin. For a whole-home installation, always confirm the final sizing with a licensed electrician. See how we build our guidance on our How We Review page.
How to use the result
The recommended size is your target for running watts and starting watts combined, with a 20 percent buffer so the generator is never maxed out. If you plan to add appliances later, or you want quieter operation under load, size up to the next step. For deeper guidance, read our full walkthrough on how to calculate generator size and our guide to what size whole-house generator you need.