What size generator do I need for 200 amp service?

"200 amp service" is printed on a lot of main breakers, and it sounds like it needs a giant generator. It doesn't. Here's why, and how to size one that fits.

What 200 amps actually means

Your panel's amp rating is the most the main breaker and the service wires can carry. It's a ceiling, like the top speed on a car's speedometer.

• 200 A × 240 V = 48,000 watts. That's the panel's limit.
• Your real load is far lower. It's built big so the range, dryer, water heater and AC can all run on a hot day without tripping the main.

You'd never run all of that on a generator in an outage. So the panel size tells you very little about the generator you need.

Panel size vs what you'll really run

Panel	Panel's limit	Typical portable generator plan
100 amp	24,000 W	Essentials: 3,000–5,000 W
200 amp	48,000 W	Essentials plus one or two big loads: 5,000–10,000 W
400 amp	96,000 W	Usually a bigger home: 10,000 W+, or a home standby unit

The limits are simple math (amps × 240 V). The plans come from the load examples below, using Champion's chart and our calculator.

Size to your running load

Pick what you need during an outage, then add it up. Using our calculator's figures:

What you run	Running W	Starting W	With 20% headroom
Fridge, 1/2 HP sump pump, furnace fan, lights, Wi-Fi, chargers, TV	2,445	3,595	about 2,950 / 4,350
The same, plus a 1/2 HP well pump and a microwave	4,445	6,445	about 5,350 / 7,750
Essentials plus a 3-ton central AC	5,945	8,445	about 7,150 / 10,150

The central AC row uses Champion's upper figures for 3 tons: 3,500 running and 6,000 starting watts.

A worked example

The calculator above is set to the middle row:

• Running: 400 (fridge) + 1,000 (sump) + 700 (furnace fan) + 100 (lights) + 15 (Wi-Fi) + 80 (chargers) + 150 (TV) + 1,000 (well pump) + 1,000 (microwave) = 4,445 W
• Biggest surge: the well pump, 3,000 − 1,000 = 2,000 W
• Starting: 4,445 + 2,000 = 6,445 W
• With 20% headroom: about 5,350 running and 7,750 starting watts

That fits a 7,500 W class generator with a 240 V outlet. See what a 7,500 watt generator can run.

Use your electric bill as a sanity check

Your bill shows how much energy you use in a month, in kilowatt-hours (kWh). Divide by the hours in a month to get your average draw:

• Formula: kWh per month ÷ 730 hours × 1,000 = average watts
• Example: 900 kWh ÷ 730 × 1,000 ≈ 1,230 W average

Your peaks are higher than the average, because the AC and the water heater switch on and off. But it shows how far below 48,000 W a normal home runs. An electrician can do a proper load calculation if you want an exact number.

The hookup limits you, too

A portable generator doesn't feed your panel through 200 amps of wire. It connects through a 30 or 50 amp inlet and cord, so the outlet caps what it can send:

Generator outlet	Most it can carry
L14-30 (30 A, 120/240 V)	7,200 W
14-50 (50 A, 120/240 V)	12,000 W

So a 10,000 W generator on a 30 amp L14-30 hookup can only send 7,200 W to the house. If you're buying a big unit, match it with a 50 amp inlet. See 30 amp vs 50 amp generator cords.

Transfer switch or interlock for a 200 amp panel

Both are safe, code-approved ways to connect. Both must be installed by a licensed electrician.

• An interlock kit fits your existing panel. It's a sliding plate that blocks the main breaker and the generator breaker from both being on. GenInterlock says you pick the kit by your panel's brand, model and main breaker rating (100 A, 150 A, 200 A and so on).
• A manual transfer switch has its own small panel for chosen circuits. Champion's 50 A switch, for example, has 10 circuits.

Our interlock vs transfer switch guide covers the pros and cons. Never backfeed the house through a dryer outlet or a wall outlet. Generac warns it can send power back down the utility lines and kill line workers.

What about a standby generator for 200 amp service?

A home standby generator is fixed in place, runs on natural gas or propane, and switches on by itself through an automatic transfer switch. It can be sized to cover the whole panel. That's a job for a dealer or installer, who sizes it from your loads. This guide is about portable generators, where you choose what to run.

Quick rules

1. Ignore the panel number when sizing. Use the load you'll run.
2. Add the one biggest surge, then 20% headroom.
3. Get a 240 V outlet if you have a well pump, central air or want to power the panel.
4. Match the inlet to the generator: 30 A for up to about 7,000 W, 50 A above that.

Safety: Run it outdoors only, 20+ feet from the house, away from windows and doors. Read our carbon monoxide guide.