100 A vs 200 A service: which one does my house need?
It depends on the appliances, not the square footage. A 1,600 ft² house with gas heat, hot water, cooking and drying calculates to 59.0 A under the NEC 220.82 optional method (100 A minimum), comfortably inside 100 A. The same house all-electric with 12 kW of baseboard heat calculates to 102.3 A (110 A minimum), and 118.3 A (125 A) once a 40 A EV charger is added. Under the more conservative standard method the all-electric house needs 175 A. In practice, a gas house is fine on 100 A; anything all-electric belongs on 150 or 200 A, and 200 A is the default for a new service because the cost difference is small.
Updated September 23, 2026. Numbers on this page are computed by the same engine as the calculators, under NEC 2023.
Worked example: 1,600 ft² all-electric house, optional method
Calculated per NEC 2023Optional method (220.82)
Inputs
| NEC edition | NEC 2023 |
|---|---|
| Floor area | 1,600 ft² |
| Small-appliance circuits | 2 |
| Laundry circuits | 1 |
| Cooking | Electric range 12 kW |
| Clothes dryer | 5,000 VA |
| Appliances fastened in place | Dishwasher 1,200 VA; Garbage disposal 900 VA; Built-in microwave 1,500 VA; Electric water heater 4,500 VA |
| Heating | Electric resistance 12,000 VA in 6 units |
| Air conditioning | 3,000 VA |
Result
| Calculated load | 24,560 VAfrom 49,400 VA connected |
|---|---|
| Calculated current | 102.3 Aat 240 V |
| Minimum service rating | 110 A240.6(A) standard rating, not less than 100 A |
| Line item | NEC | Connected | Demand | Basis |
|---|---|---|---|---|
| General lighting and receptacles | 220.82(B)(1) | 4,800 VA | (in subtotal) | 1,600 ft² × 3 VA/ft² |
| Small-appliance and laundry circuits | 220.82(B)(2) | 4,500 VA | (in subtotal) | 3 circuits × 1500 VA |
| Appliances fastened in place | 220.82(B)(3) | 8,100 VA | (in subtotal) | 4 at nameplate |
| Ranges, ovens and cooking units | 220.82(B)(3) | 12,000 VA | (in subtotal) | 1 at nameplate |
| Clothes dryers | 220.82(B)(3) | 5,000 VA | (in subtotal) | 1 at nameplate |
| Permanently connected motors | 220.82(B)(4) | — | (in subtotal) | None |
| Other fixed loads | 220.82(B)(3) | — | (in subtotal) | None |
| EV supply equipment | 220.82(B)(3)a | — | (in subtotal) | None |
| General load after demand factors | 220.82(B) | 34,400 VA | 19,760 VA | First 10,000 VA at 100%; remaining 24,400 VA at 40% = 9,760 VA |
| Electric space heating at 40% | 220.82(C)(5) | 12,000 VA | 4,800 VA | 40% of 12,000 VA (6 separately controlled units); largest selection |
| Air conditioning and cooling | 220.82(C)(1) | 3,000 VA | 0 VA | 100% of 3,000 VA; omitted, heating selection is larger |
The general load reaches 34,400 VA connected and is reduced to 19,760 VA; the six baseboard units count at 40% under 220.82(C)(5). 102.3 A rounds up to a 110 A minimum, which in the real world means a 125 or 150 A service.
Three versions of the house, both methods
Calculated per NEC 2023Optional method (220.82) and standard method (Article 220 Part III)
Inputs
| Gas heat, water, range and dryer | 15,900 VA connected |
|---|---|
| All-electric (12 kW baseboard, range, dryer, water heater) | 49,400 VA connected |
| All-electric plus a 40 A EV charger | 59,000 VA connected |
Result
| Gas heat, water, range and dryer: optional | 59.0 A100 A minimum |
|---|---|
| Gas heat, water, range and dryer: standard | 52.3 A100 A minimum |
| All-electric (12 kW baseboard, range, dryer, water heater): optional | 102.3 A110 A minimum |
| All-electric (12 kW baseboard, range, dryer, water heater): standard | 151.2 A175 A minimum |
| All-electric plus a 40 A EV charger: optional | 118.3 A125 A minimum |
| All-electric plus a 40 A EV charger: standard | 201.2 A225 A minimum |
Fuel choice moves the house from 59.0 A to 102.3 A; the charger adds another 16.0 A. The standard method is higher on every version because it takes electric heat at 100% rather than the optional method’s 40%.
What the two ratings buy you
A 100 A service supplies 24,000 VA at 240 V; a 200 A service supplies 48,000 VA. The rating is the ceiling on calculated load, not on the number of breakers: a 100 A panel can have 30 spaces and a 200 A panel can have 20. What you are choosing is how much connected load, after the NEC demand factors, the house may carry.
The step between them is not free but it is not large either. The service conductors, meter base and panel are bigger, and the utility may need to change its drop or transformer connection. Most of the cost of a service change is labor and permitting, which is the same at either size, which is why electricians default to 200 A when a change is happening anyway.
When 100 A is genuinely enough
The gas house above calculates to 59.0 A with air conditioning, a dishwasher, disposal and microwave. It has 9,840 VA of calculated headroom on a 100 A service, enough for a modest EV charger or a hot tub. Houses like this were the norm before 1990, and there is nothing wrong with keeping them on 100 A.
When you are really choosing 200 A
The moment electric heat or a heat pump with strip heat enters the picture, the calculation moves past 100 A in almost every house. Add an EV charger and it moves past 125 A. Between 150 and 200 A the decision is usually about the future: a second EV, a heat pump water heater, an induction range. Two hundred amps absorbs all of those; 150 A may not.
If the existing service is 100 A and you are adding one load, the NEC 220.83 existing-dwelling method (see the EV charger answer) is a gentler test than the numbers above, because it gives the existing loads a 40% factor past the first 8 kVA. It is worth running before assuming an upgrade.
Frequently asked questions
- Is 150 A a real option?
- Yes. 150 A panels and meter sockets are common, and the all-electric house above (110 A minimum under the optional method) would fit one. The price difference between 150 and 200 A equipment is small enough that 200 A is usually chosen anyway.
- Why do the two methods disagree by so much?
- The standard method carries electric space heating at 100% and the range at its Table 220.55 value, while the optional method takes 40% of multi-unit baseboard heat and everything else at 40% past the first 10,000 VA. On the all-electric house that is 151.2 A versus 102.3 A. Both are code-compliant; the permit states which was used.
- Does a 200 A service make my bill higher?
- No. The service rating is capacity, not consumption. Some utilities charge a one-time fee for a larger service connection, but the monthly bill depends on kilowatt-hours used.
- Can I upgrade the panel without upgrading the service?
- You can replace a 100 A panel with a 200 A panel for more breaker spaces, but the main breaker must stay at 100 A unless the service conductors, meter and utility connection are upgraded too. The calculated load still has to fit the main breaker rating.
Related questions
- How many amps does a house use?Calculated service current for four typical houses under the NEC 220.82 optional method, from a 1,200 ft² gas home to a 2,600 ft² all-electric one, and why the appliances matter more than the square footage.
- Can a 100 A panel handle an EV charger?Often yes, if the charger is sized to the house. A worked NEC 220.83 calculation on a 1,400 ft² house, gas-heated and then all-electric, shows which Level 2 charger sizes fit a 100 A service.
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