The number of breakers you can add to a panel is equal to the number of unused slots visible at the front of the panel box. So the panel shown above can handle three additional 120-volt breakers. That’s the simple answer. But if you need to add more circuits than you have available slots, it gets a little complicated. 

   There are breakers made half-height, so that two circuits will fit in one open slot, called tandem breakers. You can also replace an existing breaker with a tandem and get one additional breaker in each location in a full panel. Some panel manufacturers do not allow tandems, others only allow them in a limited number of locations, and some permit them anywhere in the panel. To learn more about this option, go to our articles What is a tandem circuit breaker? and What is a CTL breaker? 

    There is also a limitation of the total number of breakers that the panel is rated for by the manufacturer, which you can find on the data sticker at the inside of the panel door. What is the maximum number of circuit breakers allowed in an electric panel? covers the details of this issue.

    And you should only add new breakers in a panel that are produced by the same manufacturer specifically for the panel, or ones by another manufacturer that have been UL-approved for installation in your panel. Just because they fit snap onto the bus bar and fill the slot neatly does not mean they are safe and will function properly. For more on this, go to Can you add circuit breakers by different manufacturers to an electric panel if they fit? 

    There's one other option, although it can get expensive: have an electrician install a subpanel connected to the existing panel. It will need two slots in your existing panel, but allow you plenty of additional circuits.

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Field Guide for Home Inspectors, a quick reference for finding the age of 154 brands of HVAC systems, water heaters, and electrical panels, plus 210 code standards for site-built and manufactured homes, and the life expectancy rating of 195 home components. Available at amazon.com for $19.95.
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Here’s links to some of our other blog posts about ELECTRIC PANELS:

• What causes copper wires to turn green or black in an electric panel?  

• When should a corroded or damaged electric panel cabinet or disconnect box be replaced? 

• When did arc fault circuit interrupter (AFCI) breakers first become required?

• My circuit breaker won't reset. What's wrong?  

• What is a split bus electric panel? 

• What is the maximum gap allowed between the front of a recessed electric panel box and the wall surface surrounding it? 

• What are the requirements for NM-cables entering an electric panel box?

• Why is a fuse box/panel an insurance problem for homebuyers? 

• What is the difference between GFCI and AFCI circuit breakers? 

• Why are old electrical components not always "grandfathered" as acceptable by home inspectors?

• What happens when you press the "TEST" button on a circuit breaker in an electric panel?

• What is a Dual Function Circuit Interrupter (DFCI)? 

• What is the difference between a Combination Arc Fault Circuit Interrupter (CAFCI) and an Arc Fault Circuit Interrupter (AFCI) circuit breaker?  

• What is the difference between "grounded" and "grounding" electrical conductors? 

• What does it mean when a wire is "overstripped" at a circuit breaker?  

• Who is the manufacturer of those "bad" electric panels?

• Why is the circuit breaker stuck in the middle? 

• What is a double tap at a circuit breaker?

• What is the life expectancy of a circuit breaker? 

• Why do some breakers in my electric panel have a "TEST" button on them?

• What is the right size electric panel for a house? 

• What do I need to know about buying a whole house surge protector? 

• • • • • • • • • • • • • • • • • • • • • 
Field Guide for Home Inspectors, a quick reference for finding the age of 154 brands of HVAC systems, water heaters, and electrical panels, plus 210 code standards for site-built and manufactured homes, and the life expectancy rating of 195 home components. Available at amazon.com for $19.95.
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• What is the maximum height you can mount an electric panel above the floor? 

• What is the code required clearance in front of an electric panel?

   Visit our ELECTRIC PANELS page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.