How to Find Your Main Breaker Size

Your main breaker size is the number stamped on the handle of the large breaker at the top (or bottom) of your electrical panel — usually 100, 125, 150 or 200.¹ That number, not the label on the panel door, is your service size, and it's the first thing any panel capacity check needs.

Where to look

1. Open the panel door, not the inner cover. The door swings open; the metal cover behind it (the dead-front) stays on.
2. Find the biggest breaker. It's a double-wide breaker, often set apart from the rest and sometimes labeled MAIN.
3. Read the number on the handle. It's molded or printed on the handle end: 100, 125, 150, 200.

If there's no large breaker inside, check outside next to the electric meter. Many newer homes have a combined meter and main breaker outside, with the inside panel acting as a subpanel.

Why the panel label can mislead you

The sticker inside the door lists the panel's bus rating — the most current the panel itself can carry. Builders often install a 200 A panel with a smaller main breaker, or a 125 A panel fed by a 100 A main. The breaker is what limits your service, so it's the number to use.²

What you see	What it means
Main breaker handle says 100	Your service is 100 A
Panel label says 200 A	The panel could carry 200 A with a bigger main and service
Meter base has a breaker	That breaker is your main; the inside panel is a subpanel

What to write down while you're there

• Main breaker size.
• Number of breaker spaces, and how many are empty.
• Whether the label allows tandem (half-size) breakers.
• The panel brand and model from the label.

Our free Panel Capacity Worksheet has a table for exactly this, so your electrician gets the same numbers you do.

Next step

With the main breaker size in hand, you can see how much of your service your home actually uses. Adding up the breakers won't tell you — here's why.

Technical notes

1. Berkeley Lab notes that service panels are generally referred to by the size of the main breaker; common sizes installed today are 100 A and 200 A, and legacy sizes include 60 A and 80 A. In California, roughly a third of single-family homes have panels of 100 A or less. Sources: LBNL technical brief, 2024; LBNL, California panel study, 2024. ↩

2. The main breaker is the service overcurrent device, so a load calculation compares the home's demand with its rating, not with the panel label. Sources: NFPA 70 (NEC®), free access; LBNL technical brief, 2024. ↩