So I think I answered my own question. I used a residential load calculator and came up with 77 amps minus the a/c (on its own circuit at the main). With the current 90 amp service, I should be ok, assuming the calculations are correct. Right?

On another note, why would I have a 90 amp breaker main service disconnect with a separate 30 amp for the a/c? 120 amp service?

Just to clarify, I looked at the wiring at the main. Service comes from the meter to these two breakers which are stacked on top of each other, with one wire connecting to each side (right and left) of these stacked breakers. Wiring to the sub panel leaves the 90 amp breaker up and out of the panel, with grounding going to a bar. The a/c wiring leaves the 30 amp and drops out the bottom of the panel going to the a/c, with grounding to the bar. A single copper wire leaves the bar out the bottom of the panel (I assume going to a grounding rod).

Assuming your load calculations are correct, you are probably right at capacity with 100A service. Note the size of the main breaker does not necessarily mean that is what your service size is.

It was not uncommon in older panels to have several large breakers (range, AC, etc) and then a "lighting main" that feeds the part of the panel with all the branch circuits for the receptacles and lighting. The code permits this provided there are no more than six breakers throws to shut everything off.

If you're adding bigger kitchen appliances, especially induction cooktops, you may indeed want a larger service. If for some reason (like you're out of spaces for breakers for the new kitchen circuits) you are going to upgrade the panel, the additional costs of upgrading the service may be worth it.

Thanks for the info. I figured that the size of the main service disconnects didn't necessarily indicate my actual service. How do find out what my actual service is? Power company? Is 120 amps a common service level (30 for the ac, 90 for the rest) or is it reasonable to assume I might have 125 or 150 amp service? I ask because if my service can handle going from the 90 amp to 100 amp to my sub panel, that would give me 25% over my anticipated household load.

Pretty much you do have to ask the power company.
Common sizes are 60,100, 200, 400 though other sizes aren't unheard of.

So i called the power company (pg&e) and they said that for my address i have not more than 320 service amps comming in to my meter. I am confused because i figurd i would have a fixed service level. Does this mean i can upgrade my 90 amp main breaker to 100 amp, as long as my wiring is of correct type and gauge? Do i need to involve my power company if i make this change?

The wiring coming in from the utility is NOT your service entrance. It is the utility drop.

What you have on your house is your limiting factor. You have either a 100, 150 or 200A service in most cases.
You do not add up the 90 and 30A breakers to call what you have a 120A service.

If the home is newer you may have had a stickler for an inspector which is why you were limited to a 90A breaker instead of the standard 100A since that feeder does not serve 100% of the load.

Why would you possibly need to go from 90 to 100A??

Well going off my calculations, I do not need to go up to 100. At this point I am just trying to figure out what my service level is. The house was built in 79, no tag. When you say "what you have on your house is the deciding factor," what do you mean?

I mean the service cable, meter pan (NOT the meter itself), service entrance cable and main panel/disconnect all determine the service size.
The overhead wire from the utility is almost irrelevant.

Gotcha. Thanks. One would think it would be easier to know your service size. I know this is hard to understand without a pic, but after talking to a buddy that is an electrician, he mentioned that this panel that I am calling my main, which is to the right of my meter might not actually be my main service disconnect and actually be a sub panel. Below my meter is a cover that states do no open or something similar and he said that in there might be my actual service disconnect. I am not home to check but does this sound like common practice?

You need to find an older electrician who understands the panel you have, and he may be able to tell you how figure out the total amp rating. Younger electricians will only be familiar with what they have installed.

My story: My house had a old 150 amp panel. There was a 60 amp lighting main breaker and space for about 12 lighting/outlet breakers, and then an area for several 240 volt breakers. However, there was no 150 amp main breaker, which really confused younger electricians. Since there was no main, you also could not shut off power to the bus for the 240 volt breakers. Even the house inspector I hired made a comment about the panel being "wrong". However, the electrician I hired for my heavy up was very familiar with this type of box. He said it was completely correct and legal when installed, and I could have waited for the 200 amp upgrade if I thought 150 amps would work.

Bruce

Even younger electricians recognize a split panel like that if they are competent. Even today you have to be able to compute a load. The problem is that your young guys entire experience comes from building tract houses where they don't have to think about what they are doing.