"How many amps do I have" is the question people ask. It is the right question, but only about half of what actually decides this.
Four things decide it: your service amperage, whether you have free breaker spaces, the age and make of the panel, and what you plan to add. A 100-amp service with room to spare is fine for a gas-heated house and tight the moment you add an EV charger or a heat pump. And two specific panel brands are a reason to replace regardless of capacity.
Find out what you have
Open the panel door — the outer door, not the cover over the wiring — and look at the large breaker at the top. The number on it is your service size.
- 60 amps — very old, and inadequate for a modern house
- 100 amps — common, and workable for many homes without large electric loads
- 150 or 200 amps — the usual range for newer or upgraded homes
- A fuse box rather than breakers — old enough that replacement is generally advisable
While the door is open, count how many empty breaker slots you have. Capacity in amps and physical room for new circuits are separate problems, and you can run out of either.
The signs that genuinely indicate a problem
The main breaker trips. Not an individual circuit — the main. That means the whole house is drawing more than the service can supply, and it is the clearest capacity signal there is.
No empty slots. You cannot add a circuit without somewhere to put it. Tandem breakers sometimes help, but only if the panel is rated for them.
A fuse box. Fuses work, but the panel is old, replacement fuses invite the dangerous habit of fitting an oversized one, and insurers increasingly ask about them.
Visible heat damage — scorching, discoloration, a burning smell, or a panel warm to the touch. Stop and call an electrician the same day.
Buzzing or crackling from the panel.
Lights dimming when large appliances start. Occasional slight dimming can be normal; pronounced or worsening dimming is worth investigating.
The signs that usually do not
One circuit tripping repeatedly. That circuit is overloaded or has a fault. It is a circuit problem, not a service problem, and an upgrade would not fix it.
A GFCI or AFCI outlet tripping. They are doing their job. Repeated tripping means find the cause, not increase the service.
Wanting more outlets in a room. That is usually a new circuit, not a new panel — assuming you have a spare slot.
Federal Pacific Electric (FPE) Stab-Lok and Zinsco panels have documented, long-standing problems with breakers that fail to trip under fault conditions. A breaker that does not trip is the one component in your house whose entire purpose is to prevent a fire.
Replacement is widely recommended for these regardless of amperage or apparent condition, and some insurers ask about them. The brand name is printed inside the panel door. If you find either, that finding outranks everything else on this page.
What actually decides it: the load calculation
Amperage alone does not answer the question, because what matters is your simultaneous demand, not the sum of everything you own.
Electricians perform a load calculation following the National Electrical Code, which accounts for square footage, fixed appliances, heating and cooling, and applies demand factors reflecting that not everything runs at once.
That calculation, not a rule of thumb, tells you whether the service is adequate. Ask for it in writing — an electrician who recommends an upgrade without performing one is guessing, and it is an expensive guess.
The loads that change the answer
These are large, continuous, and the usual reason a previously adequate service stops being adequate:
- EV charging — a typical Level 2 charger draws a substantial continuous load
- Heat pumps and electric heating
- Electric ranges, ovens and dryers replacing gas equivalents
- Tankless electric water heaters — see tankless vs tank
- Hot tubs, pools, workshops
- Home battery or solar systems
If you are converting a house away from gas, expect this question to come up. Electrification is the single most common reason a 100-amp service becomes limiting.
The middle options nobody mentions
An upgrade is not the only answer, and it is worth asking about these before agreeing to one:
A lower-amperage EV charger. Charging overnight rarely needs maximum speed, and a smaller charger may fit within your existing service.
Load-management devices that prevent two large loads running simultaneously — often enough to add a charger without upgrading the service.
A subpanel, if you have capacity but no physical slots.
Correcting the real problem, if the symptom is one troublesome circuit rather than a genuine shortage.
What to do
- Read the main breaker and count your empty slots
- Check the brand for FPE Stab-Lok or Zinsco
- Look and listen — heat, scorching, buzzing
- List what you plan to add in the next few years
- Get a load calculation in writing before agreeing to any upgrade
- Ask about the middle options above
This is general information, not professional advice. Electrical work carries real risk of fire and electrocution and is regulated — see our disclaimer.
Frequently asked questions
How do I find out what amperage I have?
Look at the main breaker at the top of the panel — the number printed on it is your service size. Common values are 100, 150 or 200 amps.
Is 100 amps enough?
For many homes with gas heating and cooking, yes. It becomes tight once you add electric heating, an EV charger, a heat pump or a workshop, because those are large continuous loads.
Do frequent breaker trips mean I need an upgrade?
Not necessarily. A single circuit tripping usually means that circuit is overloaded or faulty. Needing an upgrade looks more like the main breaker tripping, or no space left to add circuits.
What panels are considered a safety concern?
Federal Pacific Electric Stab-Lok and Zinsco panels have long-standing documented reliability problems with breakers failing to trip. Replacement is widely recommended regardless of capacity.
Does adding an EV charger require an upgrade?
Often, but not always. A load calculation decides it, and there are lower-amperage chargers and load-management devices that can avoid a full service upgrade.
Sources
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