Service size is the maximum current, in amperes, that a home's electrical service can deliver from the utility, set by the service conductors, meter base, and main breaker. Common residential sizes are 100, 150, and 200 amps, and an NEC Article 220 load calculation determines how much connected equipment a given service can support.
Why it matters to you
Service size limits how many large electric loads, such as central air, a heat pump, an electric range, a dryer, or an EV charger, the home can run without an upgrade. At 240 volts, a 200-amp service is rated for 48,000 watts, twice the 24,000 watts of a 100-amp service.
Practical guidance
Read the number stamped on the main breaker handle, usually at the top of the panel, to learn your service size. Before adding a major electric appliance or EV charger, have an electrician run a load calculation, because an upgrade usually involves the utility as well as the panel.
100 vs. 150 vs. 200 amp service: what each typically supports
| Service size | Rated capacity at 240 V | What it typically supports |
|---|---|---|
| 100 amps | 24,000 watts | Smaller or older homes with gas heat, gas cooking, and few large electric appliances |
| 150 amps | 36,000 watts | Mid-size homes with central air plus one or two large electric appliances, such as a range or dryer |
| 200 amps | 48,000 watts | Larger or all-electric homes with a heat pump, electric range, dryer, and water heater, often with room for an EV charger after a load calculation |
How do I find my home's service size?
Look at the main breaker, usually the large breaker at the top of the panel, which is stamped with its amperage. The panel's label lists its own maximum rating, which can be higher than the main breaker. If the panel has no main breaker, an electrician can identify the service rating.
Is 100-amp service enough for a home?
For a smaller home that heats, cooks, and dries clothes with gas, it often is. It gets tight when central air, an electric range, an electric dryer, and an electric water heater are all present. Adding an EV charger or a heat pump usually calls for a load calculation first.
When does a home need a service upgrade?
Common triggers are adding an EV charger, switching from gas to a heat pump or electric appliances, a remodel that adds circuits, or a panel with no open breaker spaces. Frequent main-breaker trips or lights that dim when large loads start are also reasons to have a load calculation done.
Does upgrading to 200 amps mean a new panel?
Usually. A service upgrade typically involves a higher-rated panel and main breaker, larger service conductors, and often a new meter base, with the utility disconnecting and reconnecting power. Replacing the panel alone does not raise service size unless the conductors and utility supply are upgraded too.