Decision Guide
100-Amp vs 200-Amp Service: Which Does Your Home Need?
Published August 27, 2026 · Updated August 27, 2026
Short answer
100-amp service covers most homes running gas heat, gas water heating and one AC system. You need 200 amps when the NEC Article 220 load calculation exceeds 100 amps, which typically happens at three or more large electric loads: central air, electric range, dryer, water heater or EV charger.
The honest test
Count your large electric loads. Central air conditioning, electric range, electric dryer, electric water heater, EV charger, hot tub, pool equipment, second AC system, garage apartment.
Two of those on 100 amps is usually fine. Four or more almost never is. Three is where the calculation actually has to be done rather than guessed.
Note that gas appliances change the answer completely. A house with gas heat, a gas range and a gas water heater has far more headroom on 100 amps than an all-electric house of the same size.
What the calculation actually does
Under NEC Article 220 a dwelling load calculation totals general lighting load by square footage, small-appliance and laundry branch circuits, fixed appliances, the larger of heating or cooling, and then applies demand factors that account for the fact you never run everything at once. The result is a number in amps, and it is compared with your service rating.
This is why square footage alone is a bad proxy. A 1,600 square foot Uptown double with two three-ton condensers and an electric range does not need the same service as a 1,600 square foot Lakeview ranch on gas heat. Any contractor who quotes 200 amps without asking what is in the house is quoting a part number, not a design.
When 100 amps is genuinely fine
- Gas heat, gas water heater, gas range
- One AC system
- No EV, no hot tub, no pool
- Panel in sound condition with open slots
If that describes you and the panel is not a Federal Pacific or Zinsco, leave it alone. A service upgrade you do not need is $2,000 to $4,500 of nothing.
When you need 200 amps
- Adding an EV charger and the calculation says the service cannot carry it
- All-electric or mostly-electric appliances
- A second AC system, common in converted-attic houses here
- Adding a garage apartment, workshop or major addition
- Panel is full with no room to add required circuits
- A standby generator interconnection the current service cannot support
The middle options people skip
A subpanel, $400 to $2,000. Solves "no open slots" when the service has capacity but the panel does not have room. This is the right answer far more often than it gets offered.
A single dedicated circuit. If the problem is one window unit tripping one overloaded circuit, that is a dedicated circuit, not a service upgrade.
Load management. For EV charging specifically, devices that shed or throttle the charger when household demand peaks can avoid a service upgrade entirely.
Panel replacement without a service change, $1,200 to $2,400. If the issue is an obsolete or corroded panel rather than capacity.
What each costs
| Job | Range |
|---|---|
| Panel replacement, same amperage | $1,200 - $2,400 |
| 100A to 200A service upgrade | $2,000 - $4,500 |
| Subpanel | $400 - $2,000 |
| Panel relocation, added on | $800 - $4,000 |
| Permit | $50 - $300 |
What about 400 amps?
Rare in residential and usually the wrong answer. It comes up for very large homes, properties with a substantial detached structure, or multiple EV chargers plus full electrification. It is a materially bigger job than 200 amps, involving different service equipment and frequently a utility conversation about the transformer. If someone is proposing 400 amps for an ordinary house, ask to see the load calculation.
Bottom line
Do not buy amperage by intuition. Count your large electric loads, and if the answer is three or more, have the NEC 220 calculation done before you take bids. We do the calculation before quoting, and if a subpanel or a single dedicated circuit is the honest answer, that is what we will tell you. Call 504-336-6748.
Related questions
Will 200-amp service lower my bill?
No. A panel distributes power, it does not consume or save it. What an upgrade buys is capacity, modern overcurrent protection, AFCI and GFCI coverage, and a system your insurer will write. Be careful with anyone who claims otherwise.
How do I find out what service I have?
Open the panel door and read the rating on the main breaker: it will say 100, 125, 150 or 200. If there is no main breaker and you see screw-in fuses, you likely have 60 amps, and that is a replacement conversation regardless of load.
Can I upgrade later when I actually need it?
Yes, and often you should. The exception is when you are already opening the service for another reason, because doing the mast, meter can and panel in one visit is meaningfully cheaper than doing them twice.