HowMuchIt / Generator
What size generator do I need?
A generator has two numbers on its label: running watts, what it can keep up, and starting watts, the short burst it can give. Motors need that burst to start, so the right size covers both.
Work out your generator size
| Step | How |
|---|---|
| 1 | Add the running watts of everything that runs at the same time |
| 2 | Find the one item with the biggest starting surge |
| 3 | Starting watts needed = step 1 + that item's extra start-up watts |
Sump pump: the two charts print 1,000 / 2,100 and 1,050 / 2,150 watts; we use the higher pair.
Running watts and starting watts
A lamp or a toaster draws the same power from the moment it is switched on. A refrigerator, a pump or anything else with a motor needs a short burst, often two to three times its running power, for a moment while the motor starts. The makers' rule is simple: add the running watts of everything you want to run at the same time, then add the biggest of those start-up bursts. You do not add every burst, because motors rarely start at the same second. The appliance's own label or manual gives its real figures; charts are a starting point.
Safety first, every time
A generator's exhaust carries carbon monoxide, a gas you cannot see or smell and that can kill in minutes. Run it outside only, never in the house, the garage or the basement, even with the doors open, and keep it at least 20 feet from doors, windows and vents. Connecting a generator to a house's wiring is work for a licensed electrician, with a transfer switch.
Before you buy
- List what you truly need in an outage: fridge, sump pump, a few lights, phone chargers.
- Leave some room above the total, so the generator is not running flat out.
- Check the outlets on the generator match your cords and plugs.
Good to know
- Running watts are the steady power needed to keep an appliance going. Starting (surge) watts are the extra burst needed for a moment to start a motor.1,2,3
- Motor appliances such as refrigerators and pumps can need about 2 to 3 times their running watts to start; simple heating loads such as lamps and toasters do not.2,3,4
- Sizing rule: add up the running watts of everything you will run at the same time, then add the single largest starting-watt figure.1,2
- Two maker charts list a refrigerator/freezer at about 700 running watts, with 2,200 in the starting column.4,5
- A 1/2 horsepower sump pump runs on roughly 1,000 to 1,050 watts and needs about 2,100 to 2,150 to start.4,5
- Chart figures are approximate. The appliance's own label or manual gives its real watts.3,5
- Never run a portable generator inside a home, garage, basement or any enclosed space, even with doors and windows open.4,6,7
- Outdoors, keep the generator at least 20 feet from doors, windows and vents.7,8,9
- Generator exhaust contains carbon monoxide, a poison gas you cannot see or smell that can kill within minutes in an enclosed space.1,6
How we checked this page
Checked on October 26, 2026. We kept a fact only when two independent publishers agree, and each one is numbered to its sources below. Where sources give different numbers, we keep only what they share. We never write a price. This page was written with an AI assistant and checked against the sources below.
Sources
- Owner's Manual & Operating Instructions, model 46592, Champion Power Equipment
- What Size Generator Do I Need?, Generac Power Systems
- The Power to Perform (2023 Europe Power Products), Briggs & Stratton
- Safety Guidelines Generators, Honda Canada (Honda Power Equipment)
- Generac Portable Generators RS5500 / RS7000E brochure, Generac Power Systems
- Portable Generator Safety Alert (5123), US Consumer Product Safety Commission (US federal)
- How to use a generator safely, Texas Department of Insurance
- Use a Generator Safely (PSA toolkit), Centers for Disease Control and Prevention (US federal)
- Portable Generator Safety Tips (Taylor County Extension blog, 2017), University of Florida IFAS Extension