How to Find Your Home’s Electrical Service Size

The four numbers, in the order you can actually check them

Steps 1 through 3 take about ten minutes with the panel door open and a flashlight. Step 4 is not something you do at all — it explains why, and who to ask instead.

1. 1
   Read the main breaker rating — the most reliable number, when it exists

   Open the panel’s outer door. Do not remove the dead front — the inner cover the breaker handles poke through. The main breaker is usually the largest handle, set apart from the rest at the top or in its own small section, and its ampere rating is printed on the handle or the breaker body itself. This is the number to give an electrician when they ask what service you have, because it describes the device actually limiting what can flow into the panel today. Two things can make this step return nothing: some panels are main lug only (MLO), with no main breaker at all because the disconnect lives elsewhere — a meter-main outside, or a breaker in another panel upstream — and some labels are too worn to read. Either way, do not guess; move to step 2 or step 3 instead of writing down a number you inferred.

2. 2
   Read the panel’s own label — its number is a ceiling, not a diagnosis

   Inside the door, the manufacturer prints a label stating the panel’s catalogue number and its own current rating — what electricians call the bus rating, the maximum the internal busbars are built to carry. A panelboard’s own supply-side overcurrent device is capped at that rating under NEC 408.36, so the bus number can never be smaller than the main breaker — but it is routinely larger. A 200 A-rated interior fed by a 100 A or 150 A main and a matching smaller service is a normal, deliberate installation: it lets a future service increase skip a panel replacement. If the bus label reads higher than the breaker you found in step 1, that gap is the panel’s built-in headroom, not your current capacity — quote the breaker number, not the label number, when anyone asks what you have today.

3. 3
   Check the meter base rating as an outside, independent confirmation

   The meter socket — the round or rectangular enclosure the utility’s meter plugs into — carries its own ampere rating, stamped on a nameplate on the enclosure or visible through its window. This is a genuine cross-check, not a decoration: NEC 230.66(B) requires a meter socket to be "listed and rated for the voltage and current rating of the service" it belongs to, so a legitimately installed socket’s rating should match what the service was designed to carry. It is read entirely from outside — you are not opening the enclosure or breaking the utility’s seal, both of which are illegal to do yourself in most jurisdictions. One exception is worth knowing: a socket the utility itself supplies and exclusively controls is not required to be listed at all, so on the rare service built that way this check may not apply.

4. 4
   The service-entrance conductor size is the real limit — and it is an electrician’s check, not yours

   Everything upstream of the panel is protection and labelling. The wire itself — the service-entrance conductors running from the meter to the main disconnect — is the actual physical ceiling on how much current the house can draw, and it is also the one figure on this page you cannot determine by looking. Conductor ampacity (NEC Article 310), including temperature correction and the terminal-temperature limits that decide the real answer, is not quoted numerically on this site. It is a design question with more inputs than any web form has, and a wrong number there is a fire. On top of that, the conductor does not even have to match the breaker: NEC 310.12(A) permits the service conductors for a 100–400 A one-family dwelling service to carry as little as 83% of the disconnect’s rating — so a main breaker stamped 200 A can legally sit on conductors ampacity-rated for roughly 166 A. Reading the gauge stamped on the insulation and looking it up is not enough on its own; the same wire’s allowed ampacity moves with its insulation type, the termination temperature rating at each end, and how many other conductors share its raceway. This is exactly the step where "call an electrician" is not a disclaimer — it is the honest answer.